Re: 67 xr brakes help/diagnosis
I take it you still have the single system master cylinder? The XA front calipers and XY rear drums have larger cylinder diameters than the standard XR disc/drum setup, hence more peddle effort is needed to stop the car. A larger diameter master cylinder is needed, and a later model larger one requires a fair bit of work to make it fit. I was running a simular setup to yours on my XR and I had the "low pedal feature" XR master cylinder which has a slightly larger diameter than standard. There was also 2 types of booster on the XR's, vh40 and vh44. One is bigger than the other (can,t remember sorry) which will give more boost assist when braking. This did help a bit but my brake peddle still needed a good hard push to brake. In saying this the XR GT had both of these so you should have them anyway.
I have seen an XW booster and master cylinder fitted to an XR. The booster mounting plate and that part of the firewall had been cut and welded into the XR. A bit of work though. I have also seen the duel system XT master cylinder fitted to XR's, but not sure if this would help.