My last combination with a 266 at .050 SFT cam worked with...
- 1200 RPM idle
- 25* initial
- 35* total
- full advance around 3000
- carb had all four plates drilled with ~ .110" holes
- no vacuum advance, although it would have probably been helpful at my 3500 highway cruise RPM

I have a loose converter, but a stick car is going to be more prone to low-RPM detonation under a load. Otherwise, your option of locking out the distributor and dialing back the timing when starting sounded reasonable.