Dan, I think the numbers are correct as I have found a main case for sale on ebay, just can't confirm what it is out of. The box I have is pretty crusty but I'll try and get a decent pic and post it.
http://www.ebay.com/itm/Muncie-3-speed-T...A-/361373686207
The only other info I have been able to find is on the Buick board where a guy's son has a '70 GS with what he believes to be the original 3 speed still in the car and it has the same 3952662 main case and 3911942 tail housing casting numbers. If this turns out to be correct then the vin on my box would have to be a restamp unless the same box was used in a Buick?
Post #18
http://www.v8buick.com/showthread.php?90...48ff80374cbb0c2