big block in a 64 dart

hi we bought a pretty clean 64 dart & i have a medium built 400 & 727 sitting around . so we figure we will put them in it we also have a 440 virgin block that we bolted to the 727 to use for mockup to get the motor & trans plate first time putting it in place the trans hump looks to tight we beat the firewall seam flat already i have not gotten back out to the shop to check any further . does anyone have pics or suggestions . thanks dave