Bob, if you're still there, I'm sorry that it's taken me three days to respond. I know that I've been a bit of a pest about this, but I'm happy to report that I now have succeeded in cross referencing the Sharp PC-900 opto-isolator which is illustrated in the MIDI electrical specification to the Fairchild H11L1M. I'm sure that the 6N138 would work just fine, but since the H11L1M seems to be just what I was looking for, I've decided to go ahead and use it.
I appreciate you explaining about the five milliamp current requirement, and, after locating my MIDI reference, "The Musician's Guide to MIDI", I have noticed that the author, Braut, does indeed make mention of this himself.
By the way, what I have in mind is something which is probably relatively simple - at least, compared to what it might have been. I will be building a portable MIDI file storage box, which I will use to download files from my computer. I will then use the box as a music keyboard controller. The idea is to save me from lugging my desktop computer around.
Thanks for the help, guys, and I'll keep you posted on my progress. Mike "Chip Monk" Mandaville