MPG Motor Magnum vs. Hemi

I tried to build this engine with LPG in mind, so a healthy compression ratio, polished chambers and ports, full length headers, cold air intake and Edelbrock AirGap to keep the charge cool.

The stall convertor is a big 12"(?) unit made in the '60s (non-lockup, for stock 727s out of a C-body).
I have driven the car shortly with a different A518 with Lock-up in between, which had a 11" convertor. I could notice by how the engine revved in Neutral at the time, that the convertor was lighter, compared to the 12" convertor I had before and after this again (The Lock-up 518 ate its OD-unit so I had to swap it out again for the non-lockup unit I still had).
I hope the A500 I have (to be rebuild) will add some mileage.
The cam I'm currently using has very little lash (hydr.cam w/ solid lifters) at just around .008", which tightens up a few thou when the engine warms up. This is ofcourse to take up the lash while the lifter is still on the 'ramp' of the lobe and prevent clatter and shorten valve train life.