13x7's on a 93 TC Executive Series STUD LENGTH question?

Have a set of 13x7's for my 93 Towncar Executive series. I am running 1/2" spacers due to the fact the inner diameter of the adapter is to small to fit over the bearing hub/ caliper rub. They clear the calipers and bolts perfectly. My problem/concern is I can only get 3/4 of the nut threaded onto the stud, thus increasing my chance of stripping the threads on the studs and also immensely increasing my chances of bending/breaking the studs due to the fact i cannot safely get the nut torqued to a tight and safe spec. My question is what stud length is needed to get a lug nut length onto the studs allowing me to keep the adapters tight and worry free but not too long that they hit the inside hub on the rims?

Any and all help greatly appreciated!

Thanks
KC

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