proportioning/metering/distribution valve clarification

AFAIK none of these should have any restriction or metering of the front lines. I don't know what application that particular part (MBM-etc) is supposed to fit, but it wasn't a 1968 disk brake car. It says "60s-70s", but I'm sure it never went on a 1960s A-body, and probably not any A-body.

The 69-74 part will work with your combo, if you can source one that doesn't leak (there was a bad batch out there). I did the 9" drum to K-H disk swap on my 67 Barracuda, so I can vouch for that.

My other 67 had factory K-H disks, and it had the separate PV, but that would be a lot more difficult to retrofit, since you'd need to cut and flare brake lines (or bend the too-long one and hope it doesn't break, and source a short connector piece).

Actually, my advice is to buy all new front compartment brake lines while you are at it, since you are draining the system anyway, and you need the correct fittings for the dual line disk brake MC. The old lines will be brittle as heck, and the threads will be rusted.