IMM Iron heads on that Mag 318

Would the IMM heads and an RPM airgap be too much in a dart sport with 323 gears? Want a good streetable car. Was just thinking that after getting factory heads rebuilt I could just up the coin for the IMM heads. I would use stock heads if they didnt need any serious money dumped into them.

These heads:
http://immengines.com/indyimmironheads.html

Thinking of the following:
323 gears in an 8 1/4
Magnum stock shortblock with cam reground by bullet if necessary
Custom convertor to match everything
2.74 low first gear non lock up 904 trans.
Holley Vac Secondary carb sized for combo.

Thanks