I have the twin to that Jazz - a sunburst 1976 with maple neck and black blocks. As it arrived with a dead neck pickup (which the seller, Jugghaid, was totally upfront about), I popped in some DiMarzio Model J's and this thing just rocks! While I was in mod mode, I added a J-Retro, Hipshot Ultralites and a Schaller 463 bridge. Between the purchase price and all of the goodies, I have about $600 into this bass and I think that it smokes basses that sell for double and triple the price. So much so, that I felt no hesitation selling my Epiphone Jack Casady and Reverend Rumblefish PJ as this bass was making them collect dust as it became my absolute #1.
So long as the mods you make are reversible and cause no major visible structural changes, feel free to mod.