I have a similar setup, I'll post pictures soon as I make it look pretty
I recommend you completely remove the stock fuel filter, I got so annoyed trying to find filters for it and take it on and off without spilling a pint of oil each time. I'm filtering to 10 micron then dumping it straight into the stock tank. I'm using cheap $5 clear inline paper filters (think big riding mower filters) Being paper they will crud up pretty fast. But thats okay since they are cheap and they catch alot more crud than the plastic mesh filters you'd usually see.
I'm willing to bet its a standard 3/8" pipe thread to replace the 'banjo' bolt that is connected to the steel hose. So you can thread almost anything you like in there. If you have trouble getting a good seal you can use copper/alu washers to pinch off any leaks. If you do this just be mindful of the filters getting clogged and worst case the injection pump pulling enough vacuum to pinch/crush the the rubber house and cut off the fuel. It will starve for fuel and putter out.
I've logged a few hundred hours now on a very similar setup! looks awesome!
Your motor is more classy than mine, Mine is the 1929 clone (I think), I think this one is older?
And sorry if you did by-pass the stock filter already.