If you are serious about fun only, it would be no fun to build a 500" engine and then start breaking clutch and driveline parts. I would use the parts you have and add h-beam rods and forged flat-top pistons. now you have a shortblock that will live through missed shifts and a shot of nitrous if you so desire. I recommend Rob Nixon at Smythe Automotive for any machine or assembly work you may need.