There's a forum i read ages ago somewhere about using newer model boosters and master cylinders on early commodores.
From memory here's basically what the popular mod to do is:
Use a VS plastic booster (bolts to firewall same as early but is bigger diameter and may not clear rocker covers if you have an early v8, will fit vn headed rockers if you have the vn top end)
you need to cut down the push rod 5mm into master cylinder.
Master cylinder's that fit VS booster is VS and VT types only. You want the VT 1-1/4" large bore quick fill master cylinder (this combo is a must for using big brakes on early commodore, without this mod you wont have the pedal feel or master cylinder strength to operate big calipers)
Pedal rod needs to be cut down and a new locating pin hole drilled.
I can't remember the measurements off hand but it's something you can do by dummy fitting and measuring anyhow.
$60 gets you 3 brass fittings to fit your brake lines to the new master cylinder (vs vt use different pipe flare to early vb-vl)
Back to the VR booster you're using, I'm pretty sure you still have to trim down the pushrod into the master cylinder and also shorten the pedal rod same as using VS booster.
On one hand with the VR booster you can use your old 1" master (not much of an improvement of braking performance or pedal feel)
On the other, if you use VS booster which will fit the VT master cylinder you'll need to spend more to get it all done but it'll be worth it as it paves the way to handle big brakes later down the track.
You can use a vt booster but you'll need to make your own bracket to fit it to the firewall and still shorten your pedal rod.
I'll keep hunting to try and find the original thread i learn't all this from
