Will this be an issue?
 

So, my 64 has a early 70s (according to cap.)brake booster, mc & prop valve. The mc is for a disc/drum set up and the prop vale will be removed due to that's a no no with a all drum setup. My booster is good. I got the correct mc and I'm replacing all the brake lines.

My question is, will I have a problem with the booster push rod length due to longer push rod hole in the drum mc vs the shorter hole in the disc/drum mc? I though about cutting a piece of rod to slide in the drum mc to take up the slack though I'm not sure that's a good idea.

Re: Will this be an issue?
 

You will need 10# residual valves. The disc/drum MC could have one on the drum side, but not the disc side. I put mine in-line.

Re: Will this be an issue?
 

I'm keeping the drum/drum set up for now so the new drum mc should have the res valves and I shouldn't have to install anymore. On my 56 belair when I converted to front disc brakes, I installed a willwood #10 res valve on the drum part of the system.

Re: Will this be an issue?
 

Yes a drum/drum MC should have the residual valves. The disc/drum MC you had would have worked fine with a residual valve, but it does look different.