I've seen a few of those odd double digit numbers on T-10s, but I haven't been able to tie them to anything that made sense.
As for the trans not having a VIN stamp, all Corvettes in '63 and hi-perf passenger cars (300hp & up)were "supposed" to have the VIN stamp.
While it's possible that the St. Louis Corvette line skipped stamping that one, I'd think it's much more probable that the trans is from a 250hp 327 passenger car. IT's also possible that it's a service replacement trans.
Thanks for the input.
Verne