Thank you Bear. That is exactly the type of information I am looking for.
Without sounding too needy
can you direct me to a reliable source for these, and other related specs and tolerances?
The whole thing is a process. You start with making some choices: which cam are you going to use, and with rocker arm ratio are you going to use? Everything follows from those two choices. The relative "aggressiveness" of the cam lobes combined with the amount of lift determines how much spring pressure it needs in order to keep the lifters riding on the cam at all times. To get the full picture you also have to choose a maximum operating RPM for the engine and make sure you never exceed that. The higher the RPM, the stronger the tendency is for the cam lobes to 'throw' the lifters off of the cam, and the more spring pressure is required to not allow that to ever happen. Your cam vendor must supply all this information - detailed cam specs and the spring pressures (both closed and fully open) needed to control it. They should also want the details on which lifters you plan to use. Heavier lifters = more inertia = more spring pressure needed.
Once you know the spring pressures you need at both open and closed states, the next step is to determine valve lift using the combination of cam lobe lift and rocker ratio (and valve train type --- solid lifters always require some amount of "gap" - valve lash setting - that has the effect of reducing total lift at the valve and thus spring travel). You need to know valve lift in order to get springs that 1) have to proper open and closed pressures and 2) are capable of providing the required valve travel without either going into coil bind or being "too far" away from coil bind. Usually there will be more than one set of springs that will 'work', so you have to choose based on other qualities such as quality, cost, and required spring installed height. Spring installed height is the distance between the bottom of the valve spring retainer and the surface the bottom of the spring sits on (the spring seat). It's determined by the combination of valve length, spring retainers, and locks. If the distance is too great, the springs won't produce enough pressure to keep everything under control. If the distance is too close, spring pressures will be too high (which tends to wear out parts quicker) and you also run the risk of driving the springs into coil bind (where the spring 'stacks up' solid) and/or having the bottom of the retainers hitting the tops of the valve guides -- both of which tends to break parts and destroy engines.
There are special cutters for removing material from the head's spring seat surface if the measured installed height is too close, and there are shims you can put under the springs if they need to be 'shortened' (however shims are only available in a few standard thicknesses so sometimes in order to get your installed heights 'perfect' you have to do both - cut the spring seats by a small amount so that a shim will 'bring it back' to the correct height).
Once you have all the installed heights correct, you have to check to make sure that the retainers don't contact the valve guides or stem seals at full lift. There are special cutters to trim the tops of the valve guides too, if needed.
Once you have all of this correct --- the right springs installed at the right height to provide the right spring pressure and with just enough travel with respect to coil bind and parts interference --- you're still not done.
Now you have to fit rockers and pushrods. You have to choose a pushrod length that does two things: makes the best possible contact patch on the valve stems throughout the full range of valve lift and also ensures that the rockers have adequate clearance between them and all the other parts - i.e. the spring retainers and the purshrods themselves - throughout the full range of motion. Some builds with solid lifters benefit from using pushrods that restrict the oil flow to the top of the engine also, if that control isn't being provided by some other means, so that's a consideration too.
Plus -- if you're running 1.65:1 rockers then you have to make sure the pushrods don't rub anywhere in the heads. It's common to have to use a grinder to widen the pushrod passages in the heads if they came from an engine that originally ran 1.5:1 rockers.
Yeah, there's a lot too it. You can't just grab any old cam and throw it into an engine and expect to get the best results. "Everything" has to be matched and fitted to work with "everything else". Sure, you can put a big old lumpy cam into any engine and make it "sound hot" as long as all you ever do is let it sit and idle to impress your friends at the local burger joint, but if you want to actually be able to drive the car, make power, and have it not self-destruct then there's a lot more work to do.