I fitted an F960 and it went straight on. There is the issue with the locating tab you should be adding, I had too little time and a bad back and it was getting dark a cold beer waiting so......
There are no other screws on the mating surface, this is a pic of the top of Bagusjeep dizzie. You can see the holes at 3 and 9 o'clock the cap adapter screws on to, that previously the old cap was fastened to.
Perhaps if you posted a pic?
BagusJeep lives in Bali, the Land of Temples.
With a Jeep every prayer counts.
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys