I own an R2, a C2, C3 and two R-4's. The Clipper 2 is new to me and I have not "tested" it as of yet. My C 3 breaths almost as well as a DA. My R -4's aren't bad either. As mentioned, keep the original hose loop for posterity and use a USD hose loop with it. Even the Dacor 1.5 inch mouth piece systems were IMHO "klunky" and did not breath very well. The Dacor first stage diaphragms were probably pretty nice back in the day. However, after sitting around for 60 years they are stiff as a board. Unfortunately, there are no modern replacements. The good news however, with some use these old HP diaphragms do regain their flexibility. Don't judge the reg on one dive.... or even two or three. In my experience, it takes around four or five dives to get the reg functioning well.
If you go BY THE BOOK you will have success. The reg must be positioned between your shoulder blades and against your back for true success. You should swim in a slightly heads up position. If you do that, the reg will breath well and you will enjoy it. It's a darn shame we live so far apart. I'd like to help you along with the project. Dacor's get a bad rap by those who don't give them a proper chance and don't dive them the way a double hose should be dove. A Kraken, a built up RAM, DA or a Mistral are all VERY nice regs and are also forgiving to those who insist on diving them with a BC or even a modern backplate. These systems tend to have the reg ride behind your head and to far behind your back. With a VDH back plate, or a repro Klauda harness you will have your double hose in the orientation it was mean't to be and you will get the most out of it. You may never dive a single hose again!
I wish you the best of luck with your R -4 project! I hope you have half the success I have. If that's the case you will really enjoy it.