Everyone has an opinion, so here is mine!
If I was updating an RB-1 to have brifters, I'd probably start by looking at the stock build sheet of the '93 RB-1/8:
Brakeset: Shimano 600 Ultegra brakes, levers
Shift Levers: Shimano 600 Ultegra STI
Crankset: Shimano 600 Ultegra, 40/53 teeth
Pedals: Shimano 600 Ultegra clipless
Rear Cogs: 8-speed, 12 - 23 teeth
Seatpost: Kalloy, SP-248 220 mm
Saddle: Avocet racing 1, leather
Handlebar: Nitto, modified #165, deepdrop

I have a '92 RB-1 (with the bar-end shifters) and man, it is just the greatest. I've been contemplating doing what you're doing (buying another frame to build up a bit more modern), sounds fun.