Hi, did some numbers on the Syncro low gear, 20mph freewheeling with trans
in gear gives about 7900 RPM for the clutch disc. Pop goes the .... 

Doubtful any damage to the gearhousing, no real torque being transmitted.  I
think it's the low gears under load trying to spread themselves apart that
wrecks the housing, the reverse idler gear is on a smallish shaft passing
through a thin web section in that housing, so reverse may be the culprit.
Any Syncro owners with a busted housing want to check where it broke? tx,
bye, tim