So a big breakthrough yesterday. It moves again.
The tranny was causing the engine to stall. Motor would run fine until you put it in gear and it would limp under high revs and cut out very easily.
Switched the carb from original Rochestor to the Edelbrock that came with the new engine. No Change. : (

So over the last week and a half I fitted a transgo shift improver kit and a new B&M torque convertor.
While I was at it I fitted new poly trans and engine mounts and did some work on the dual sidepipes exhaust welding and adding flexi sections.

I think the problem was that I didn't fit the original torque convertor properly. It wasn't pushed back onto the second set of splines enough so it was pressing on the flywheel and stalling the engine. At least thats what I think was happening.
I also polished up the bellhousing when I had the tranny off.
The van is moving now and not stalling. There is a leak from the tranny so I need to change the front oil seal (kicking myself for not doing it when the trannny was off - it looked fine) and then do some more engine tuning and it then should be good to go.
Go on to the next piece of the project that is...... bodywork.
79 chevy G30 cobra camper conversion.