I just spotted this on eBay. Isn't this a very
early (pre-S/360) IBM
board?
eBay item #230231322529
While it is weird to have SLT on an SMS board, it is well within
reason. SMS (the form factor for the board at auction) was used for 25
some years.
The part number (397563) puts in pretty much in the S/360 era.
--
Will