If you decide to go 5.7l, I can give you the info with what I did on mine. First choice to make is on the block. I picked up a used 1996 truck block but the casting date code is actually 1995. Determine whether you want a roller cam and lifters. If so, study up on the block and roller cam/lifter notes. If the block is not machined for a roller setup, it requires special lifters with a bar across them. If it is machined, then you need "dog bones" to keep the roller lifters from spinning. Careful with used Vortec Heads, they may be cracked. Mine were and I had to replace them.
If you go this route, I can give you the part numbers for everything I bought, however, I haven't yet fired mine off on the engine stand (but very soon). I targeted mine at 300Hp since I have an Alpha One Gen One drive and targeted compression for 87 octane pump gas (this is a cruiser).