Build a 528 or 543?

I like the longer rod 4.15 kit myself. A short rod engine will want serious ports, which is why I think smaller might be better for you. You will need a new convertor because the the engine is not the same one that was in front of it before. It also might be a good idea to have it broken in and dyno'd prior to ordering that convertor. I'm not a hardcore racer... but my understanding is the 2500lbs mark is the "magic" 'glide window. Above that you may be quicker with another gear, below it you'll be faster with only two speeds and a kick *** convertor letting the engine pull. I really would stay away from a huge RB with a real block. You're going to spend to either buy a real block, or get a factory one reliable at that level. Sounds like fun either way tho.