I installed one of these CPP booster setups on my 49 3600 and share your frustration. I ordered over the phone and nobody asked me what transmission I was running (or more to the point, if I was running the original linkage/original crossmember); and I was sure lit up when I realized that none (that I could see) available were intended to be used with the original linkage and crossmember.
I did as others indicated above, just moved the whole assembly back and made up a longer pushrod from tool steel (love the lathe man). That was in 2020 I believe, and it's been working fine since I did not cut the crossmember and I'm running the oem brake and clutch linkage (with a T-5 but that's beside the point).
Thought for sure I had pictures of the linkage after the install, unfortunately apparently not. Next time I'm under there I'll try and remember to grab one.
And at the end of the day - this is such an easy (but time consuming!!) fix, WHY does nobody simply make a kit to work with the OEM crossmember?
Edit: as an aside, I have cleaned up that brake line routing since - that was the initial plumbing
