In replacing the front brake lines on the '69 I've found out that the disc brakes are not original to the car. I also now realize there is no proportioning valve at the master cylinder or on the frame. I've been driving the car like this for almost 5 years without any issues. The brakes have always worked great and I've stood on them a couple of times but not what I'd call a panic stop. My question is should I install the valve? Is this a potential safety issue? I'm not concerned about correctness I just don't want problems that could be avoided.

Does it have a combo valve instead? If it doesn't, I'd install one. You don't want to find out if you should have had it when it's too late. It's a small price to pay.

I swapped out to power disc/drum set up from 4 wheel manual drum and kept the old valve. I have "tested" it on a back road or two and have no issues. If you been driving like this for 5 years, might be fine. But as you said ,better safe than sorry.

I'd put a new one in it or add an adjustable valve in the rear for more adjustability.....- The proportioning valve not only balances\ sets the pressure ratio front to rear, it will also keep pressures from spiking if you do a panic stop...

Thanks for the replies. I guess I'll get one on order.

The best detailed explanation that I have read on what a proportioning valve really does, and why you should have the correct one:
http://www.stoptech.com/whitepapers/proportioning_valves.htm

Might be the best thing to do, adding one. But wouldn't it only be good if you had the same size tires/wheels all the way around? If your running skinnies and steamrollers I would add an adjustable one.

Well I laid out $125.00 for a repro from Ricks. I hope it was the right thing to do. I've got 215's front and 245's rear. It will be a couple of weeks before I get the front suspension back together before I can test.