96 Rivi owner here.

95 Rivis and Bonnevilles were Series I L67s with the M62. 96+ Had the M90. The 95s and 96s had the 4T60E (vacuum and electric hybrid) while 97+ got the 4T65E-HD. That's why 96 3 vacuum ports. The fuel rails are also slightly different between 96 and 97+, but you can use a 96 blower on 97+ and vice versa. You just need to dick with the vacuum lines or just transfer everything over from your old blower to the new one. Throttle bodies were the same in 96 and 97+.