750 Cylinder head on a 650 engine?

Because I'm running f*cking amateur hour over here. I ended up with 2 cylinder heads off Ebay, not paying attention, I later realized that one is for a 750, however it's much cleaner than i head I got for the 650, can I use the 750 head on a 650 engine?
I'm replacing the old the old head because a couple of the carb intake boot bolts broke off, and I cant manage to extract them.

 

That depends. Are both YICS heads?
If so then yes you can, however there are differences in the cams. Which 650 and which 750? Seca or Maxim?

If you want to keep your old head, make a dam out of modeling clay around each boken bolt. Mix up a solution of alum and warm water. Fill the dams with the solution and wait. In a few days the broken bolts will be in soultion and you will have clean threads to use.

 

Both heads are from 1982 model Maxims, which are same as mine. If there are differences in the cams, should I take the cams and shims out of my old head and throw them on?

 

Here ya go. From : The Information Overload Hour

b) all XJ650 (except, perhaps, for the Turbo models), XJ700 non-X, and XJ750 model cams will interchange. Here's the lift variances between them:

Intake:

* 650 models (except Turbo): 8.50mm
* 700 non-X models: 8.80mm
* 1981-83 750 models: 8.80mm
* 1984 XJ750RL models: 8.80mm

Exhaust:

* 650 models (except Turbo): 7.80mm
* 700 non-X models: 8.30mm
* 1981-83 750 models: 7.80mm
* 1984 XJ750RL models: 8.30mm


You can swap your intake cam (check clearances with plastigauge to be sure you have a good fit), or just run the head as-is and retune the carbs to suit (more lift should get a slight increase in flow even though you have a smaller displacement).

If you swap the cam you'll need to re-do the valve clearances on that cam entirely. The relationship between the valve stem cam lobe, shim bucket, and shim all affect valve clearance. If you go that route just swap the cam and check clearnaces.