I don't know about an M38, but I have the same set-up (327 on a T-90) in
my Willys wagon and at minimum, have to replace the syncro's every 4-5K
miles and complete rebuild every 8k. This is even when keeping loads
and acceleration as light as I can. The T90 is a very light duty
transmission to bolt to a V8, with the inertia of a heavier clutch plate
and the higher torque. The M38 may be not be as much of a problem
though, since it is quite a bit lighter in weight. But, I would guess
most of the trashing of yours came from the V8.
Just my 2 cents,
Charles Schultz
Scottsdale, AZ