If you pick up 75 hp like we did on this motor then you should easily pick up a couple of tenths if not more. It will depend on how much power capability the motor has. This was a flat tappet motor that were shutting off around 6500 rpm. If it was a roller motor that was turning 7500 rpm I bet the HP difference would have been even greater.
Switching from the cross ram to the X box will add some power but you'll probably need to change gears and maybe upgrade the valvetrain to take advantage of the new power.
I'd think the 750 carbs would work fine on the X box. I ran 800's since that is what I had but I can't see why the 750's wouldn't work just as well.
The biggest problem is getting the tune up correct. It is kind of a pain to deal with twin Eddy carbs! It is a lot of little clips, levers, springs, rods, etc everytime you pull the tops. I can see where a guy would get tired of twisting screws if you had to do a bunch of trial and error to get the cross jetting correct. At some point I'd put studs in the top of the Eddy carbs just to keep from stripping out those screws.
