Your MT-32 will work fine with any game, including Sierra's, intended to be played on an old-style MT-32.

Thank you very much for the quick reply, I was getting nervous about spending money for nothing!

Even if you did obtain the "wrong" module, it is much less common than the "right" module, so I'm sure you could sell or trade it for what you want.

I guess, but I'm a sucker when it comes to this kind of stuff...
It's very hard for me to get rid of stuff like this, if I really had no use for it it would end up sealed in a cupboard.

But anyway, is there a specific game I could try to make sure? One that would sound odd from the start in an obvious fashion?
Also, if both an old MT-32 and a new MT-32 are hooked to the same BOB, it would be necessary to turn one or the other before launching a given game?

As I understand it, newer games on old MT can hang the computer, older games on new MT-32 might sound odd?

No, AFAIK the MT32 cannot hang a computer as the midi just gets put out but nothing is looped back. You can just "daisychain" the MT32s by connecting one to the computer and the other via the midi thru port of the first one.
You just need to replug the music output on your system or use a mixer to chose either MT32

As you just want one or the other it wouldn't even be hard to make a box with a single DPDT switch to select as you could leave the ground wires connected together or absent entirely.

Expect some latency on the MT-32 furthest away, this is why nobody producing mused ever used the Thru sockets but it should be good enough for what you want to do.

Learning something new everyday, thank you both for your help!

Wasn't HoC one of the games that took advantage of early MT-32 glitches?

This should give you an audio reference to help you confirm what module you have :

https://www.youtube.com/watch?v=OLvsaJ4h-VY

Listen at 2:09:15 with Space Quest I VGA and if the "SpaceAlvin" sound is cutoff, then you have a new-style MT-32.

Thanks a bunch! I'll make sure to check this out once I get the module.