Hello again, I'm in the planning stage of a potential brake system reworking. It's for a 66 122s.

I want to replace the MC with a dual-circuit setup and have found this:

https://www.jegs.com/webapp/wcs/stores/servlet/productitem_10001_10002_756327_-1_125210

Nictalope, a member here, said it has the same bolt pattern as the stock MC in my last brake thread. The diameter is 1/8 of an inch larger than the stock MC (7/8" going to 1") so I guess I'll get a slightly stiffer petal out of it.

Here's the part where I need some advice, as I am still a novice at this type of stuff.

I want to, if possible, keep the stock front disks and rear drums as well as the calipers and pistons. It's more of a financial issue, but since I am also the one doing the work I don't want to get myself in too deep. Besides, I haven't seen a single conversion set for this model car and custom is pretty much out of question.

This brings me to another thing then: Since I plan to keep the stock rear drums, I am under the impression I will need to install a residual valve after the proportioning valve, to keep in pressure.

This is the proportioning valve I may use:
http://www.jegs.com/webapp/wcs/stores/servlet/productitem_10001_10002_744516_-1_127906
Kind of neat, I can adjust the force distribution whenever I need to.

I'd just like to know if my plan has any fatal flaws (will I need a new actuator arm?) and input from you guys' vast personal experience.

One additional thing: I've got a hydraulic issue somewhere in my system now, it's either the MC or inside a drum but I can't tell because I am waiting for a puller.

My pads and calipers as well as rotors appear solid and in perfect shape.