5.9 magnum swap

You could easily run FI Tech(example), use your LA AG, keep the true retro look while going modern in a stealthy way. If I went that way, ie "no rails", which I understand completely, I would get a 5.9 Mag short block, EQ LA heads, LA fromt cover, alt, etc. Use the Tanks Inc pump in tank with black lines and your current air filter and nobody would ever know it wasnt 340 car. It would be easy to do and not as expensive as rebuild on 340 and x heads done right...
Or you could do magnum with factory FI which would require 134 tooth flywheel with reluctor ring for your 833. The pcm(brain) can easily be installed under dash out of sight. When I build harnesses, they are very low profile, no big bundles of wire coiled up or huge fuse box, usually dont even put pcm in engine bay. Our fuse panel consists of either a 4 or 6 fuse Bosch panel 1x2 or 1x3 plus 2-4 relays, very easy to hide. As far as building a harness, best place for info or diagrams is a FSM downloaded from flea bay for $25 or used hard copy for $30-$100. You can also get a harness from us or hot wire already done.You can run stick pcm but should get it flashed to remove evap, second O2 and also any cam over about 208-210 duration.