It is 1/4" brake line and according to the 59 Shop Manual that size is correct.
Regarding the fitting kit suggestion, it looks like that one is only for cars, not the trucks and it moves the port location to the side which doesn't line up with my pre-formed lines. Out of curiousity I might order one anyway and see if I can make it work as a last resort.
I did find in the orignal parts book a listing for a 58-59 "main cylinder pipe adapter" pn 3739974 which might be what I need to find. I don't see anything on the usual parts suppliers websites for any special fittings for the 58/59 though...
