What is the right proportioning valve for my 68 stang?

I just installed a scarebird conversion(front discs), but keeping my rear drums. Is an adjustable proportioning valve necessary, how about residual valves? If they are, what is a good set-up that isn't too expensive.

Thanks

What line does the adjustable proportioning valve go?

I found multiple answers to your questions by searching the forum...

In any drum circuit you must have a residual pressure valve of 10 psi.

If you do not have a proportioning valve between the master cylinder and rear brakes (the divider block and rear brakes in 67-up), the rear drums, which do less than 25% of braking, will receive the same pressure as the front discs. This is a problem, because discs require much higher hydraulic pressure to work. The result is your front discs will do no braking, and you will die.

2+2, I don't have a proportioning valve on my 67 and the brakes work fantastic.

Hi,
Didn't the later model distribution blocks have a proportioning valve built into their distribution blocks? Also, as well as, the some of the later model M/Cs having residual valving built-in to them. It seems to me, I re-call reading about this. The valving is necessary to insure no rear wheel lock ups in an emergency. You don't want the "arse end" swapping corners!
All of this aside, I plumbed an adjustable proportioning valve into my rear drums system way back (10 yrs.) when I did my resto. Knowing the front disks were getting 900-1100 PSI, I setup the drums to get about 600-800 PSI. This insures no rear lockups and has served me well over the years. I'm also running a residual valve installed at the rear axle distribution block. I'm running the larger 10 x 2.5" drums. The proportioning valve is that black box just under the M/C.

Drum/drum MCs have the pressure valve built in. Some disk/drum MCs do and some don't/ Disk/disk doesn't.

I've seen the distro blocks that have a residual pressure valve bolted to them. Some Mustangs/Cougars had the residual pressure valve located at the rear of the car where the hard line goes to soft line by the rear axle.

I say but a T-block and a union up front and test the car somewhere safe. See if you need one. I hate the factory unit, it has caused me nothing but pain and heart ache. If you do need some sort of break bias install an adjustable aftermarket (Wilwood is a name you can trust) unit.

Are residual valves necessary ? If yes do i need one 10 psi or two 8 and 2psi?

All drum circuits need a 10PSI residual pressure valve. I've never seen an 8PSI one but that doesn't mean they don't exist.

The 2PSI valves are for disk brake systems where the master cylinder is mounted below the calipers. It keeps the fluid from draining back into the resivior.

I have disks in front and drums in rear. Disc/drum mc with booster . Which will my car need and where in the line should it go?

First off, you may not even need one. Some master cylinders have them built into the drum circuit. You should verify what master cylinder you have in there before you do anything.

Secondly, you can put it anywhere in the curcuit before the wheel cylinders.

Yeah, that last comment although true, may or may not apply. For what this is worth, I'm running a 1" MC with a 10 lb residual screwed into the rear distribution block. After which, the rear brake line screws into it.
After inserting this, I simply re-bleed the rear brakes. First the right rear, then the left rear.
Good luck with your project!