Not actually sure of the bolt pattern but the '98's wheels use a captive washer clamping style lugnut not a shouldered traditional style one so make sure if they do fit to use the proper matching lugnuts and make sure they are the new ones provided in the recall. ( I know I had a '98!). Stu
It's actually 5 on 135 mm ... very close to 5 on 5.5", but not exactly right. Use at your own peril, as the saying goes. Offset would be more positive than earlier wheels too.
F-150 didn't get 6 stud until the latest generation in 2004 model year. However there were some oddball light duty F-250s from 1997 - 2000, which were renamed F-150 HD 7700 GVW package from 2001 - 2003, that used 7-stud wheels. Similar package available on the new trucks as well.