Is there a reason from an electronics expert's point of view that installing a crystal and an IR diode would not work on a 20b the same way as on a 30b?
No, it works exactly the same way. I have done just that. The only reason against the 20b is the poor keyboard compared to the 30b.
Thanks, I will eventually try it - for the better looks of the 20b! ;-)
If the looks are what you are after, you should probably transplant a 30b keyboard into the 20b :)