Where should I be setting the timing on my basically stock 1970 383 (335HP) motor?

Car has the original solenoid type distributor but I don't have the original carb with the solenoid contact, therefore the solenoid is not functioning.

My understanding of the distributor solenoid is that it is designed to retard the timing at idle for better emissions. Therefore, when the car is started, timing is advanced to about 10 degrees and then once is starts the timing is retarded to TDC.

The Tune up spec for setting the timing is TDC for a manual trans.

Without the original carb should I just be setting initial timing to about 12 BTC as is specified for not CAP cars?

Also, to what degree does the timing need to be adjusted for today's modern day fuel blends?

Just set it up based on what your car tells you. Forget the specs. And, another thing, no two engines are ever identical, no matter what, so just time it to where it runs the best!

I'd probably start at 5 degrees BTDC and go from there.

If you don't have a dial back timing light or a degreed damper, the old 'performance' method was to advance the idle timing up incrementally until you can just begin to hear pinging (during test drives after making an adjustment) then back it back down two degrees for engine safety. This method works far better when you have a quiet exhaust. And you can do it for whatever grade of fuel you intend to run.

Unless you have to fight smog inspections, you don't want the solenoid, anyway. The way that it works is to RETARD the advance when the switch is "made" (grounded) at the carb idle.

I'd start, maybe, 10-12* BTC at as slow an idle you can get, no vacuum connected.

As suggested above, play with it a little to check for pinging, etc.

I ALWAYS liked to score my balancers with correct marks so I could instantly tell what the advance was doing, no delay light needed. Some of these lights are trouble, and are not accurate.

Thanks guys