I love strokers (and have one) but if you're going to keep the original 62 heads and want to stay inside a budget, then I'd recommend you not build it into a stroker (slight pause here while everyone on the forum regains conscousness
The reason being, those heads on a stroker motor would put your compression ratio too high for safe running on pump gas without doing other things to the motor to get it "back down".
Beyond that... making power is all about air-flow, so depending on how much budget you have here are things to consider:
* Send the heads off to have them ported by a skilled porter (I like Dave Wilcox at CVMS) - expensive but worth it.
* "More" cam - "best" profile for improvement and also retaining some street manners will be a solid roller. A roller profile will let you get more effective duration "under the curve" without having to go crazy on overlap, and not going crazy on overlap is what will keep you some street manners. Plus a later intake closing event (due to more duration) helps manage dynamic compression/cylinder pressure to avoid detonation. If you do go with a solid roller cam (the old wives tales about frequent adjustments don't really apply today) make sure you use lifters that have positive oiling to the roller axles and don't rely solely on splash from the cam. Also for a solid, install calibrated restrictors in the lifter bore oil feed passages in the block - the solids don't need as much oil as hydraulics do, so the restrictors keep more of the oil where you need it most - on the mains and rods. Your trade off on the cam is going to be the converter and rear gear. If you go "too rowdy" on the cam you'll need a "looser" converter and possibly more rear gear to take advantage of it. That's another reason for a roller and managing that overlap period. A roller profile will tend to be more civilized than a flat-tappet grind of the same lift and duration.
* Clean up and port-match the factory intake to your heads. Also separate the water crossover from the intake, otherwise as soon as you install the intake and tighten up that crossover connector bolt to the timing cover all your port-matching work will go right down the tubes.
* Zero deck the block - improves "quench" and combustion efficiency so you won't have to run as much ignition timing. (Less "negative work" in the motor) This also helps prevent detonation (and nets you a small increase in compression which a 'bigger" cam will like).
* Pistons. With those iron heads and a zero-decked block (assuming a + 0.030 overbore), and stock style flat top pistons, you'll be at approximately 10.5:1 compression. You'll find lots of opinions on this, but mine is that's too much to be guaranteed safe on pump gas. Something like these:
Icon Forged Racing Pistons
would put you around 9.7:1. That's still a little on the high side Iin my opinion) but as long as you have "enough" duration in the cam to keep cylinder pressure down (via a "later" intake closing event) you should be ok with 93 octane, a properly jetted carb (lean is very bad), and a good, efficient cooling system. "Safe" would be closer to 9.5:1. You for sure want D-shaped dishes in the pistons, not round ones, otherwise you lose the cylinder "quench" effect and that will make the engine MORE prone to detonation. Another advantage of forged pistons is they're both lighter, and have less friction due to their smaller skirt area.
* Better exhaust. "Best" will be 4-tube headers, but they're also the most pain in terms of fitment and maintenance. (I hear good things about "Mad Dog" headers on both counts and will probably try them myself when my Doug's need replacing). Next step down from there performance-wise will be the reproduction cast-iron "ram air" manifolds. You give up a little in performance, but lose -all- the headaches of headers. For some folks that's a good trade. Install a good quality exhaust system (no larger than 2 1/2" tubes front to back) with an X-crossover and good mufflers.
* Adjustable valve train. Replace the bottleneck studs in those 62's with the 7/16 screw-in studs. They're much stronger. Any cam much above stock is going to need aftermarket springs and a fully adjustable valve train (poly locks) anyway. While you're at it, replace the factory rockers with aluminum full rollers. They're lighter (less mass/stress on the valve train) and the roller bearings mean less frictional losses.
* Get your carb dialed in. Read Cliff Ruggles's book on the subject, also Lars' (member on here) excellent paper.
* Good quality aftermarket forged h-beam rods. Pontiac factory rods are 'the weak link' in the motors. By the time you have a set of factory rods tested and reconditioned for re-use, you'll have spent almost the cost of a good set of rods that you won't have to worry about. Good rods are cheap insurance, especially on a 400 that can wind higher than a 455+.
* For the rest, check out the "Building Your Short Block" chapter in Jim Hand's book: "How to Build Max-Performance Pontiac V8's". Keep in mind most of that is aimed at 455's - your 400 is going to be happy at higher rpm than a 455 for making power and a cam that is "moderate" in a 455 is going to "act bigger" in a 400.
That's my take on it. I'd recommend you also contact Jim Lehart at Central Virginia Machine Central Virginia Machine Service - Home of the Injun Engine!
. He's "the man" (he wrote the short block chapter in Jim Hand's book) and will tell you the truth - even if you don't spend money with him. However, if you want someone to 'build it for you', I highly recommend him.