No you don't have to change out the brake booster/MC but that's what makes the pedal feel and it will reduce pedal travel (which will increase with the swap). Instead of using the gsr mc, which requires flaring/bending, use the booster/mc fron an RS integra. It's only 15/16", not 1" like the gsr, but brake feel is largely improved and it's a direct bolt-on apparently, not bending or anything since it doesn't have abs. Or you can use a 90-91 civic ex MC and bolt it onto your existing booster. Bolts right up as well (also 15/16").

And you're gonna want an RS integra prop. valve too, otherwise, you're gonna be locking up different corners at different times. You need one made for front/rear discs. I think they're stamped with 4040 on them. Prop valves from abs cars won't work.