Sounds like you've solved your filter problem. I didn't get a chance to tell you that you only "need" three filters for color printing. Red Green and Blue separation filters and expose at different times through each one at a time. But there's not a lot of people who practice that technique.
Hopefully you can find the mounting kit or hack one together.
I use an Aristo grid but graded paper, I find the greenish light kind of wacky for Multigrade.