The only thing I can think of is that you might have an incorrect relay... physically larger than original, but maybe functionally correct???

If all else fails I don't think filing or cutting off the interfering retention tangs will cause any problems. The pins themselves should hold the relays in place, and they make removing the relays a PiA.

A couple of years ago I tried to remove the FP relay to inspect when I was having starting problems. I used a couple of small putty knives to carefully pry the tang slots back, so the tangs would clear, but it wouldn't budge. I recall even starting a thread here asking if anyone knew how to get the damned thing out and got no response.

It turned out the problem was the due to an internal leak in the fuel accumulator that was shorting fuel back to the inlet hose from the tank, which prevented proper fuel pressure from building up at the regulator, so no big deal.

For whatever reason, it came out came out last month without much effort.

Duke