He ya'll. I own a 1972 Ford F250 (mostly restored). I recently add a Holley Sniper to the mix. Replace almost everything on the ignition system and realized the wrong plugs were put in.The motor is a 1987 302 5.0 from a mustang, but I think the heads have been changed. I got the stock plugs for an 87 302 and they do not thread on (I even tried a thread cleaner). The plugs that were on it were NGK TR55 (which are not for 302's) and had a longer threat and a bit of a lip before the first thread. I found a stamp that read 8K14 on the head with the valve cover off but do not want to have to take the heads off to find out what they are originally from. I cannot seem to find the right plugs. Any help is appreciated.