HEI 1 Wire Dizzy Conversion in my 69 SB Dart

I would get the $45 Ningbo "ready to run" distributor (ebay). You do need an external e-core coil, but that seems better than trying to squeeze the giant "coil in cap" distributor against the firewall. GM changed to that ("small cap" distributor) in 1985. You should upgrade to an electronic Vreg, which you should have done for the Mopar ECU upgrade. You can buy such Vreg's that will fit your 1969 wiring harness (see rockauto) and some look like your black factory one.