I feel your pain man,we are all going thru this stuff,i have a set of Autometer gauges in my 91 below the radio and im super happy with them but awhile back i put a new engine in the 91 and (to me) it was a huge investment and i have a electric fan so i started getting paranoid about the fan going out and not noticing the gauge cause its all the way down there so i decided to reactivate my dash gauge so i could have 2 gauges.
Granted the dash gauge is not the most accurate but id rather have something than nothing so i decided to buy a second T housing and drill and tap it for a sensor at my work (i work in a machine shop) so i bought one of those knockoff housings, holy crap those things are junk, i returned it and took a trip to my local salvage and found one,it was filthy, a quick sandblasting and a little paint and good as new, pure old "back in the day" Ford quality .
Same story with the distributor, decided to get a new cap while doing a tuneup so i just ordered one from eBay, Chinese especial, so i get it on a Saturday and go install it and it wont fit!! I'm thinking I'm doing something wrong? so it turns out the caps diameter is smaller that the OEM mid part that goes below it, ha ha ha, car parts have a size standard like lets say a door, doors are made in certain sizes and those sizes are part of a standard home building code, i guess the people that build the cap just dont think thats important,lol
I had like 5 old caps at home and i just picked the best one and put it on, guess what? it fit!