Progressive is a bit of a tricky word when it comes to twin carbs.
Are we talking progressive primaries to secondarys, thats ok. (Even with non progressive linkage do the different carbs tip in the same?)
One carb progressive to the other is not ok in my opinion.
My new carbs are almost all eight all at once.
The carbs i run now tip the primaries just a bit before the secondarys.
I think you having unmatched carbs equals a tuning nightmare. Your a braver man than i running that set up on your engine.
But i did have quite a few twin carbs to pick from that just cost me rebuild kits and time.
The new 660s well,... they cost me an arm and a leg plus my left nut.