The starter issue isn't limited to the 360s. I think the prevailing wisdom is that you want the big energizer starter for all 360s, 520s, 550s.
-MB doesn't decide if it's 12 or 24 volts. Voltage regulator does. All 231s are 12V airframes. I've got dual 70 amp alternators (TSIO-360-MB4B), so capacity isn't a problem.
The 261 and 262 conversions are all factory 252 parts firewall forward. I think the difference between the 2 STCs was manual vs electric operation of the cowl flap. Nothing unique beyond the creative differences and quality of work of the shops doing the conversions. Mine is the Mod Squad Thunderbird 261, STC SA2445CE. Was installed by Lone Star in '98.
Things like speed brakes, extended tanks, etc are separate STCs. The mod works and mod squad -MB conversions covered the FWF change and ancillaries needed to support that. Your Monroy tanks, inner gear doors, speed brakes, dual piston calipers and on and on are all stand-alone STCs, not part of the 261 or 262 STC. My stack of STC paperwork has to weigh 10 lbs.
Only one I'm aware of without a full 252 cowling is the one in WA state that was recently for sale. It still has the 231 cowling with 2 cowl flaps and a NACA duct added for the intake.
I've got all my STC drawings, instructions, etc. So if anybody needs something from the install package, just drop me a note. As far as I know, the only STC mine doesn't have is the one-piece belly.