[68GMCCustom]

Have you already got the LY6? This is the same motor I'm using...tho I'm going carb'd with a MSD box firing the coil packs. I also ditched the VVT stuff and am running a Comp LSr cam and .650 springs. I am also using a 200-4r...and you can use your 700R4...but you might want to rebuild it with HD parts.

Big differences are the LS1 genIII setup was a 1x cam gear and a 24x reluctor wheel
LS3 genIV uses a 4x cam gear and a 58x reluctor wheel. If you're keeping the stock efi setup and ECM, you won't have to worry about it. The gen III motors use cathedral port heads...where as the genIV motors L92, LY6, LS3, etc. have rectangular intake ports. So they use different intakes to fit the rect. port heads...and are not genIII compatible. Meaning you can't use a catherdal port genIII intake on a rectangular port genIV head.