Idle Transfer Slot on secondaries?

That should be a good start. Change the base plate to the Holley and relocate the IFR to the lower part of the metering block so its submerged. Does the main body have a Tslot restrictor in the body?
Not a bad idea at all to make a hybrid out of both carbs. I’ll certainly would need a lot of hand holding going that route. I would like to continue to try and get this 650 to work first as is and learn as much as I can in the process even if it means yanking it off and on a bunch of times. This I feel is a great learning opportunity and something I have been wanting to do.

Later if I succeed and want to put the 750 in or cobble it together making a hybrid then Ill need your help with that for sure. But I am just starting and don’t want to over complicate or throw in the towel with this carb…..yet…..but great option to think about!