Dunlop list the proper flat track tires on their Oz site, so the authentic look is still available.
The big filters are foam on most old pics of genuine flat trackers.
I think there are faux air boxes around which would take a small LI battery and probably a small twin output coil too, which would clean up a couple of areas.
A back mudguard, tail light and indicators would probably be mandatory in most countries if anyone actually intends riding it on the road, and earplugs and asbestos underpants would probably be nice too.
Inlet stubs a couple of inches longer would probably match the long exhausts better, but as there doesn't seem yo be any connection between the petrol tank and the carbs any improvement would be marginal at the best!