Can I use a rd35 instead of a 36 with a spacer or thick gears on a high pinion set-up? I have the locker already but am curious....will call ARB in the morning....

As long as you can find the proper gear for it.

You can purchase thick gears for the HP60. I am running "thick" 4.88's in mine.

Last time I went gear shopping for a high 60, it was easier to find gears (regardless of ratio) to fit the high ratio (RD35) carrier, than anything to fit the low-gear-side-of-the-split carrier at all.