help with qtr extensions

your issue is not the extensions, but the stamping of the quarters. You're correct in saying it's more difficult to modify the extensions; the pot metal that they're made from is very difficult to weld/build up... you're better of reworking the mating surface on the quarter itself. I know this is lots of work, but your goung to be time ahead making them fit the quarter. When aftermarket meets OEM it's never pretty.... or should I say.. RARELY pretty. IF you ahve to, fiberglass short strand filler can be used to fill gaps on the extensions themselves, but be careful of the gasket releif on the inside mating surface of the extension, you'll need this unaltered for a correct gap and gasket placement, which is necessary to keep from bruising or "pushing" the paint at the mating surfaces when they're tightened down.

Hope this helps!

Even NOS Ford panels would require some massaging, so you'll have to get to it. It is certainly possible- These are Dynacorn quarters:

Good luck man. One of my extensions was broken when i bought my 68 FB and i ordered a stock replacement and the damn thing was soo mis aligned i said screw this and i took the stock one that was broken to my family friend who is a welder and he welded it up and then i ground it down to look like the other one. Its probably twice as heavy as the other one but you can't tell anything is wrong with it and it fits perfectly.