408 stroker vs. 500 stroker Challenge fun!!

All new, 4" small block or 4.15/4.25 RB for $5K? Never going to happen. Not for a running engine, in the car, making any sort of power. You almost have enough for a decent small block stroker with a flat tappet cam. You're about $2K light for a stroked big block, and you haven't put the rear in it yet. With a 500" and any real tire, you need a dana for long term. I just dont see it. IMO, concentrate on the body and chassis, brakes, suspension, fuel and cooling systems, etc. Stick a basic 360/727 combo in it to get it running, then consider the options. In todays world you dont need to change the K frame. So build the car, get it running and debugged, and save up some cash for the real powertrain.