What’s up Jimenez84SS! Let us know how you’re planning to build/drive your car. You can’t go wrong with either of the LS gen 3-4 motors. The Gen 5 requires some reprogramming cost, the newer transmissions will fit, but you have to do some cutting of your tunnel, aftermarket parts are more expensive too for these gen-5’s.
Which ever way you decide to go, I recommend doing research...A LOT of research on this. Make a binder with everything itemized and type out the pricing on everything. Stay organized so you don’t lose your mind.
As far as the motor/trans, find and buy a donor car or truck. You can find chevy Silverados in great running, currently registered Condition. This will make your swap a lot easier since you’ll have the things you’ll need for your swap to go smooth.
Also, if you live in California and want to pass smog, the BAR referee looks for everything stock that the donor motor came with for that specific year. Leave everything stock until you pass the referee smog inspection and after that, you can change out parts for CA CARB legal aftermarket parts (since you’ll still have to smog, but not at referee).
Forgot to ask: have you updated/upgraded your stock suspension and brakes yet? I highly recommend working and investing on this before swapping out the motor/trans. Plus, it’ll give the newer LS motors a chance to go down in price. 👍🏽🤓👍🏽