Lesson Learned.........We measured the CB900C rods at 1mm longer than CB750 OEM when we first assembled the motor. Now thinking that maybe the rods had stretched......we installed an alternate set of CB900C rods.........only to find that the units with sprayers but retaining the 15mm pin are indeed 1.3mm longer than the CB750 units:o 
.......Soooooo.....we will double-gasket the cylinder-base to retain the original clearances within 2 or 3 thousands of an inch..........only a small delay but time is ticking 
Dennis, sorry for coming in 4 days late but I don't recall you mentioning the CB900 rods before unless I missed it.
I used the same trick, double up on the base gasket to get the clearance needed on my little 154cc Honda twin LSB.
I opened it up to take CB175 pistons which would give me more cubic capacity plus a much higher compression ratio.
I knew I would run into problems with the valve clearance so drilled through a used piston I had to see how much I could take off.
The answer was not enough. I took off as much as I thought safe but it was still not enough.
Enter the double up of the base gasket and it was perfect.
A trip to the dyno told me I was making great power low down but at the expense of a big loss of revs at the top end where needed.
I was at a loss for what to do next. The motor was on the bench and I checked the tappet clearance and chain tension, all OK.
Standing back from the motor that was set on TDC, I noticed that the cam timing mark was a tooth out, quick double check and I was right. Another check on the chain tension and tappets which proved correct, I had messed up.
A quick slotting of the cam sprocket and I was in business.
You might have already taken this into account but don't make my mistake mate, it's a long way to Bonneville. Good luck.
Sam.
