New SFI magnum Flex plate coming soon.

If the stock Magnum flex plate is clearing everything and working for your 904, I'll just compare the diameters. Then we'll know if making one from a 10230 neutral balance 727 flex plate will work for you and I'll send a template.
I may not get back to mine until Saturday to compare it.
Adding that I did measure bolt patters on 10242 and 10230. Both have the large 11 1/8 inch pattern for 5/16 inch bolts on large 727 converters, and both have two 10 inch patterns for more common performance converters, one with 5/16 inch bolts and one with 7/16 inch bolts.