79 trans am pontiac 400 upgrade path

Hello guys i am new to the pontiac world, i just bought a 1979 trans am, the motor is the pontiac 400, but i have an automatic. My car was one of the few ws7 performance packages that got the automatic when they started running out of borg-warners near the end of 79,
i wanted to know if i can upgrade my engine for big horsepower or swap it for a pontiac 400 from the early 70s that made 375 hp 475tq, which is easier, which is smarter?

Frst things first. Get Jim hand's book "How to Build Max-performance Pontiac V8s" by SA Designs. it will educate you on the ins and outs of the Pontiac.
Generally, all 400s are the same. There are differences. The earlier engines had more compression (10.5-plus). By adding a pair of earlier heads ('67-'70, "large valve"), you will gain a bunch of power over the later low-compression jobs. BUT... Detonation is a very real problem. The pistons should also be "dished" to make a final static compression of 9.5:1, in order to use 93 octane gas.
Lots of goodies to make the Pontiac very powerful. If you describe your intended use, gears, etc., I can make some very specific recommendations. get the book first...

okay i am in a tight spot now, i purchased my car with the roof savagely hacked off, and i am doing a convertible project, restoring the whole car, the body was rough, a paint job is coming soon, i am redoing the interior, and the top is going to cost me a lot of money. The problem was i was very disapointed that this motor only had 220 hp, and i would like to get a little more power just for now, i will eventually go all out, but until the rest of the car is done i dont want to touch the gears or the rear end or anything, but if i found the heads on ebay for under 300 from like a ram air car or something, they will bolt up? and i have to have a shop do what to the pistons?

also where can i find that book, i want to eventually know this motor inside and out.

The book can be had at Barnes & Noble, Books-a-million, Pickwick, etc. Ort, you can get it "online" at Performance Years (performanceyears.com), Ames Performance, BOP Engineering...

There are "quirks" when crossing eras of Pontiac engines. To try to explain the whole thing takes up nearly a chapter in the book.

You can build a mild engine that makes plenty of low-end and mid-range power for little money (a relative term). It would not require changing gears or transmission.

Don't confuse that "220 HP" rating with the earlier engines over 350 HP. Yes, the early engines are more powerful, but the rating system was changed in '71, reflecting much lower HP numbers for all GM engines. The point being, the gap in power isn't as "wide" as published numbers may indicate.