You need to think out what you want before we can make any real suggestions on your engine build and other parts. Heads/Cam package can get up into the low 400HP range and still be reliable and have good street manners ( if that matters?), but once you get near the 500HP mark you really need to start doing upgrades to the short block.

If you're planning N/A, you might get by with stock pistons, but you also said you want to use a power adder, so that will require upgrading the pistons (unless you are only planning 5-6lbs of boost.). You would also want to select your cam based on N/A or boosted which can affect the engine's characteristics and would effect your stall selection.

Since the engine is out of an Imp it's a 95+ motor, has the powder rods, not the pink rods, you want to swap them out. or at the least go all ARP bolts. Likewise to get to the 500HP mark you are going to need to spin the engine fairly high (typically 6500+ RPMs) LT1s use a single roller timing chain, you want to look at either going with a GM extreme duty, or switching to a aftermarket double roller, which will also require you to convert to a electric water pump. Also at those RPMs you should also be looking at upgrading to your oiling system.

Once you have that planned out then you can look at the converter, what stall and how it's going to engage.

im not gonna use a power adder for another year, i cant afford it right now

could i get buy on the stock pistons and timing chain for now?

Stock pistons yea. Stock timing set would be cheap insurance IMO. Your already in there, replace it.

truth truth

Because I will get like 30 bajillion brownie points for this....
Check these out
http://www.ls1lt1.com/forum/showthread.php?t=22900

yeah, at the moment, i have 230 bucks to my name, and ebays taking 60 of it

and i dont have the money to get a 383