Hhmmm... lots of older and experienced embedded programmers here I see! :-)

The 8742 is a UPI - Universal Peripheral Interface. This means that it has extra hardware on the ports so that it can handshake with a microprocessor bus, rather like a standard bus peripheral.

The instruction set is the MCS48 one. So you can use any 8035, 8039, 8048, 8049 assembler. There are plenty of these still around, though you may have to blow some dust off someone's top shelf to find one.

You will know that the 7 in the type number signifies an EPROM device. If not the window will be more than a clue! :-)

The devices should program as 8748's, and we don't have a single universal programmer here that wont handle those. So I guess you shouldn't have too much difficulty locating one.