At mid 70ies you could not order pickup making parts from a online store like today. My guess is that Seymour used parts of dead pickups and did rewind these in the 59 style. So maybe the first Jazz was a T-Top, maybe the JB a jazzed up older Gibson pickup.
I own a Gibson R8 and a Tribute 50 in cherry sunburst. The Tribute is similar to the 58 Reissue but has even more shoulder. This is why i stripped the back of the Tribute‘s neck and scraped the shoulders to a thicker V neck. That means the thickness more or less the same, but the shoulders are...
A flat fingerboard exaggerates some of the shortcomings of a staggered single coil with modern strings. So on every flatter than 7.25 board the g string stands out like sore thump imo. My recommendation is to use a ssl-6 with a flat fingerboard unless you use a wound g string.