I have a '27 Model T Ford Depot Hack which was built with 12 volt system and distributor ignition. Unable to find any recommendation for spark plug gap. Anybody....???
Try several and see what it likes. I ended up with about .025 with a 6 volt VW dist on my roadster.
Generally,too wide of a gap will be ragged at the low end. Close gap will idle better but they fall off on top end. This is why Ford changed gap specs on Model A was because of lumpy idle.
I have a 24 with a 12 V. and distributor. I kept mine at about 0.030 and that seemed to be the best. Put the plugs through a Champion plug tester on a Model T coil and 0.025 didn't get as hot a spark both on Champion 25 and X's.
I am currently changing to an electronic ignition and have been told to shift to 0.040 but I think it depends on the strength of your coil. I'm going to stick to 0.030 for now.