I don't meen this in a rude way, but....

I have done 10x the swaps you have done, built 5x the motors you have.
If I say its a waste of time to check sensors w/ a voltmeter, I think I would know a little more then you on the issue.

Last thing I would worry about is a fucking tps sensor or map sensor etc.. that you can use off the SOHC motor he has in his car right now.

I would:
A. Do a leak down test if I had a compressor around..
B. Do a compression test if possible.
C. Pull the valve cover and check the valvetrain for wear...
D. If possible, pull the oil pan & inspect the bearings etc..
If D is not possible, I would simply turn the crank to ensure there is no wierd ruff spots etc.