disapoining et

What bushing is on the MSD distruibutor.

Pro-billet, I'd run the black if the engine will start easily when warmed up. If it won't start with that one, go to the 21* bushing. I'd run the engine at anywhere from 16-22 initial timing. Find the point the engine won't start easily and use the appropriate bushing.

Converter slip is about 17% which is horrible.

I'd find a decent good running 750 DP and put it on the car and see what happens. Sometimes those super fancy altered carbs are a total POS when in real world use. I wouldn't run a vacuum sec carb, just my opinion. You can get really good mileage with a DP carb, it's all in the tune up and how heavy the right foot is!