HEY I did this exact thing. I had a r151f with a chipped counter shaft so I bought an early 90's 2wd r150 transmission, used its counter shaft and swapped all of the output shaft gears onto the r151f output shaft. its all together in the r151f cases running a 23 spline transfercase and everything. hope this helps/i didn't respond too late. Just be organised and pay attention.
I have roughly 250km on the transmission since installing it, I have had no issues with it.
