64.375" 5-lug 12-bolt??

[68bowtie]

the po of my truck converted to 5-lug. the front disc brake parts are from a 71. so naturally i assumed the 5-lug 12-bolt is from a 71-72. i measured the rear wms width at 64.375". as i dig around the forum, it sounds like this should be about 63.5". i found a thread that said van 12-bolts were 64.375". but that vans didn't come with trailing arms. my rear end doesn't appear to be modified. can anyone shed any light on this? is it possibly an earlier 6-lug with converted axles? i know some years were narrower. also it has 3.42 gears, not sure if that helps.