As far as i know being a distributor rebuilder , there is NO carb that will work with the loadamatic other than the orginal.
The orginal carb used calibrated "venturi" vacuum to advance the spark, NOT manifold vacuum and no other carb would have this venturi calibration from 0 to 4" of vac based on throttle and load.
I would use Charlie on this forum for a carb rebuild as he tests each on a live engine stand.