Until recently, the necks on the 4004 series basses were a tad wider with more taper than the 4003 series basses. RIC's 4003S/5 feels rather tight for many five-string players, but a conversion of older 4004s is more comfortable. The rare 4004Cii/5 are much wider, and some of the few who have one feel it is too wide. Jeff Rath, famous for his five-string conversions, prefers the older 4004 basses for his Rick conversions.
Of course, an alternative is stringing the bass BEAD. You'll lose the high five steps you'd have with the G string, but gain the five below E. You'll have to enlarge the nut slots and probably the saddle grooves on the bridge (4001/4003).