gm overdrive transmission . what did i buy????

i bought these two transmissions the other day at a yard sale. now what were they in originaly. here are my questions:
do you have any info on them?
do they hold up good behind a sbc under good to moderate driving ?
is this a t50 ?
4 speed or 5 speed?

i have pics of the numbers of the transmissions

 

corvette 4+ box?

 

T-50 5 speed OD. Mostly used in 4 cyl and V-6 apps. From a bit of digging some 305 Camero's and Firebirds real early 80s had some. A bit light for much more than a mild 327 etc. driven with any heavy foot. Kinda like running a early Ford 39 style box ,will work driven with a bit of care. Shift pattern is a bit different.
R 2 4
L 3 5

 

what do the tag numbers mean?

 

would the t50 replace a 4 spd saginaw?

 

It looks like a Saginaw as far as the front bolt pattern, shafts, etc. The shifter will probably be in a slightly different place. So it should fit where a saginaw was.

 

They came in cars that also used Saginaw four speeds, like the Monza/Skyhawk/Sunbird/Firenza type cars.