Here's an interesting one....my newly rebuilt 350/350 SB with a 222 degree cam in my '72 auto starts and runs fine.  The battery is good and the starter turns the engine over plenty fast...but after getting it warmed up, if I stop for gas, let's say, and go to restart, it bearly turns over....like the battery is almost dead.

That's a very distinct possibility. If the engine is not "kicking back", as if too much timing, and it spins & starts ok after one revolution, I'd say there could be a starter problem.

Are you running headers???  You starter maybe getting heat soaked due to the headers.  There are starter wraps or guards that can be installed on the starter to help with this problem.  If you backoff the timing a couple of degrees, it will probably help as well.

You can also get a heat sheild to attach to the starter to help keep it cool.  Or look into a small bocy high torque starter.  These cure the problem very nicely.

Ditto on the high torque starter. Drove my 77 over a year with slow turnover when the car gets hot. Bought a more expensive starter. Problem solved.