The 58 combo will not fit without major mods... none of the engine mounts bolt in. 168 tooth flywheel means you have to convert to 12 volts. Bell housing lacks bell crank for the 3100 shifter. Clutch linkage doesn't fit... ugh!
Mate the 235 to the 216 flywheel/ bell housing. Use the 6v stomp starter (a must... the 216 flywheel has 139 teeth. Only mates to a 6v starter. Works great with a 12v system. The 58 flywheel has 168 teeth for a 12v starter only.) Then drill 2 holes in the timing cover for a 216 front mount. The unit will now bolt right on.. Modify the waterpump to clear the radiator and mount whatever tranny you want.
Little tricky figuring the geometry of the carb linkage. I had to use the linkage from the 216..
Thanks for those inputs - I hadn't posted with regard to the engine swap, thought that part was straight forward.
I'm going to post this in the engine section to invite further interaction there in this regard
The good thing about this deal is it comes with everything including transmission, bell-housing, clutch, starter and all else - manifolds, carb, etc etc
So between the two I should have most of the parts I need whichever way I go regarding an open-drive or the OEM torque tube driveline.
My system is already 12V and as you suggest the 6V starter works just fine. Cranks it over handily

I had planned to swap from bell-housing, back from the 216 if going with the original transmission and per the earlier advice, sounds like that would be the best plan.
So starter, bellhousing, clutch concerns etc should be moot
I'lll certainly be keeping those parts from the 235, should an open drive transmission swap be a consideration at a later time.
I had thought the 235 engine was already equipped for the Truck forward mounts; so the later car engine does not have those? I'll do some research on the required mod for making those holes in the timing cover (if someone has a link there to the detail it will save me a search)
I had recognized regarding the water pump, my understanding is there are adapters available for that and that was already a consideration.
Can you expand on the carb linkage? It's all cables on the 51 truck obviously - again, I have the 216 so anything from that is available - what exactly did you have to do?
Any other inputs would be sincerely appreciated.