Gotta assume a 3-speed manual and not a 3-speed TH-400, right?
The 335HP engine appears to be the same as the 360 HP engine except the slightly smaller "067" cam versus the "068" cam. It should run pretty good.
Rather than consider changing any of the major driveline components, I would first do a little work on the engine to make it more "Goat-ish."
The 2 best areas to focus on are the exhaust & carb. Pontiacs respond well to better flowing exhausts as they have poor exhaust port flow for a high performance head - that's why Pontiac built in additional duration in their cams. So, Ram Air cast iron exhaust manifolds, 2.5" pipes, and free flowing mufflers, would be my first investment. Pontiacs gotta breathe.
Next would be a rebuild of the factory Q-jet. If you have anything less, this could hurt that Goat-ish feel. Small primaries for cruisin' and good gas mileage, big secondaries for a kick in the pants feel and big power. However, the Q-jet needs to be dialed in to be optimum for your application. It can be snappy and peppy, or bog down and be sluggish.
Then I would look at the engine tune-up and engine timing. Timing is very important. Having the correct distributor advance for your engine can wake it up. The factory compression is 10.75 but it more like 10.5 so I assume you are running high test/premium gas. I don't suspect your engine will run on 87 regular without it pinging. If it does, then I would suspect that someone has retarded the timing a bunch and this will kill power and make the engine a little sluggish. But better to be sluggish rather than have engine knock and destroy a piston or engine.
If you wanted more power, then I would recommend a cam change as long as the engine is in good shape, doesn't use excessive oil or smoke. Pontiacs are torque engines and you build your engine and drivetrain for torque, not RPM. If you change gearing in the trans or rear, you raise the RPM band that you will be cruising. My '68 Lemans has the HD Dearborn 3-speed manual trans, with 3.23 gears. Had a 350CI originally and it ran OK. Rebuilt a mild/streetable 8.2 compression 400CI to replace it. Used a 110 LSA Competition Cams hydraulic cam to match the low compression. The Lemans was very Goat-ish to say the least. I even went with taller rear tires which probably dropped my rear end ratio down to more like 3.08's. The engine's torque/HP was more than enough to accomplish nice burnouts, nifty redlight accelerations, several street races, and got 16 MPG on the highway @ 65-70 MPH.