HEI distributor...

They clear pretty well in any small block Mopar in an engine bay originally designed to accommodate a big block, like the firewall well in a 1st Gen truck.
I measured over 3 1/2 inches from center of distributor hole to firewall... I don't think it's over 6" in circumference...
I'm probably gonna go all in with Speedmaster... Distributor, wires, mini starter, and 20 circuit wiring harness for $300... With possibly 40% off in a few weeks... And this distributor eliminates the need for a ignition box and coil..