I HAVE INSTALLED MANY V6 3RDS WITH NO GRINDING REQUIRED.
THE ONLY PROBLEM I HAVE SEEN WHEN CHANGING TO V6 IS THE DRIVE SHAFT FLANGE. FLANGE IS NOT INTERCHANGEABLE DUE TO PINION SIZE.
THERE ARE MULTIPLE FLANGE BOLT PATTERNS. THIS CAN BE SOLVED BY INSTALLING A NEW FLANGE THAT HAS MULTIPLE PATTERNS DRILLED INTO IT.
HOPE THAT HELPS.

BIG HELP!  LOL

Thanks for the warning, I probably would have got it home, installed it, and then been really pissed when I went to hook up the driveshaft.

So that leads to the next question - are the U-joints the same between 4-cyl and 6-cyl?  If they are, I can just take the yoke off the end of the V6 driveshaft and put it on my 4-cyl driveshaft so it'll mate with the pinion flange.

Still looking for a replacement 3rd member. That ad I referenced above was posted by some dummy who didn't include any contact info.  On lunch break now, time to start calling wrecking yards.