Hi Aaron,
I modified my 450D (bought it for $10 on ebay as faulty), I simply removed both filters, this is easiest (and cheapest) way of doing it.
For use with Canon FD 400mm f2.8, I have UVIR filter (from
Lenoptec, it pases halpha un-affected, and it is way cheaper than anything else on the market - they will even cut it to size for your application. I had it cut in round shape to accomodate drop-in filter holder for Canon FD 400mm) (see
here the whole story).
If you intend to use it with reflector, you do not need UVIR filter at all, of course.