LS1’s respond well to bolt ons, ie headers, exhaust and whatnot, but both motors are great starting engines. I am more fond of the LT1 because its an iron block, and get one out of a vette and its a 4 bolt main. Also the LT1 has insane lowend torque, but the LS1 has a much better higher end. Also during the build you have to think if you need to stay emission legal or not. a cc305 will pass emissions here, but a cc306 wont last i heard. But if you are OBD2 then you can just reprogram to make it say it passes, unliek me who gets the sniffer. If you dont have to worry about emissions the id just buy the LE3 package for the LT1, upgrade your injectors, fuel pump, a few other things and your money.
only thing for the LT1 is a hypertech which isnt worth the money. Best bet is to get ahold of pcm4less, or madtunz (i think thats their name). Or you could just get a dyno tune. If its just CAI, headers, exhaust, and maybe some other small things pcm4less is perfect, but when you get inot heads and cams, and all that good internal stuff id go with a dyno tune.