Have an old SBM circle track crank that has a GM rear flange on it, anyone make a SFI flexplate that will bolt up and fit to a 904 TF/converter combo?

Thanks

This may work for you.
https://www.holley.com/products/drivetrain/flexplates/oem_flexplates/parts/RM-946

The crank I had in my R3/W8 motor had a chevy flange. I think this was the flexplate I used. But I had a Powerglide.
It doesn't say what the convertor bolt pattern is.

I have some cranks made for Nascar that have the GM bolt pattern that I run with a 904. I had the hubs turned down to Mopar size and I might not do that again.

I also had to have the "pilot bearing" area enlarged to fit the hub on the Mopar converter. Bryant machined one crank and I had a local machine shop do the other which was a Winberg.

After many dead ends with other manufactures I had to have Meziere make me a flexplate. It does have the SFI label.

It is not perfect as it does not have quite the correct offset so I run some crank shims to make it better.

If you find a better source please let me know. You would think it would be easy to make a Mopar flexplate with a GM bolt pattern but apparently it is not.

I have attached a drawing I got from Meziere but I don't know if it properly reflects the final iteration. It had to go back at least once.

However as would be expected, Meziere was very good to work with.

Did you use a motor plate and attach the starter to it?

I used a JW Ultrabell. SBM-to-Powerglide. Starter bolted to the Ultebell. That car did not have a motorplate between the engine & trans.