Do I really need to use a porportion valve?
 

I have a 67 Camaro and I bought an after market chrome 7" brake booster, master cyclinder, and porportion valve and the master cyclinder had four outlet lines. Do I really need the porportional valve or can I just pipe the lines up to the mastercylinder? I am running a disc/drum set up and a 245/45/17 tire on the back. Is anyone running without the porportion valve?

Any help is appreciated,
Thanks

You will need a proportioning valve
 

drum brakes run about a 55 front 45 rear bias...disc are about 70 f and 30 rear. If you do not run one, the rears will lock up and it will be a bad scene.

You did not state if it was adjustable ...which I would reccommend

The porportion valve is adjustable. Do I just keep adjusting until the rear brakes stop locking up?

Yes
 

adjust it until they do not lock up. Make sure you do a really hard panic stop where it unloads the rear wheel.

I don't know if the booster makes a difference or not, but I'm running manual LS1 front brakes and rear drums with no proportioning valve. I did, however, run a residual valve between the front and back brakes. I think it depends on what master cylinder you are using. I have the Strange tandem master cylinder.

Lots of factors add up to the required front/rear pressure bias - master cylinder bore areas (if different between front and rear), brake caliper/cylinder bore areas, pad area and coefficient of friction, vehicle weight bias, front and rear tire sizes, and driving style. I suspect, however, that with drum brakes out back, a prop valve of some sort would be a very wise idea - drums typically operate at lower pressures than discs.