Other contributors have said "What is the lug pattern mm measurement for an 8 lug 1990 f-250 and will the rims off an 2003 f-250 8 lug fit on my 1990 8 lug f-250?" is the same question as "What is the lug pattern mm measurement for an 8 lug 1996 f-250?". If you believe that these are not asking the same thing and should be answered differently, click here.
on 1990 the lug pattern was 8x7.5" on the 03 it is 8x180mm, there is about 1/4" difference between the two
"unless i am mistaken" - you are correct.
the earlier pattern is 6.5 inches. converted to metric = 165.1mm.
tried it. they just don't fit. 170mm is about 5/16 too wide for a 6.5".