Theoretically, if you have the same type of brakes on the front and rear, you don't need a proportioning valve. If the rear is very light though, you probably will want one. The drum brake proportioning valve should be adequate, but adjustable ones are available.
The Speedway kits work great, but you lose the parking brake. You can get GM calipers with built in park brakes. They mount the same as regular front calipers, and they are expensive in comparison to fronts. You can find them in salvage yards on Caddy ElDorados, Camaros, and other performance oriented cars. Most people don't look at the Caddys though, so more likely to find some there at a pick-n-pull. You can also mount a second manual caliper for a park brake on the same rotor. Go cart calipers work great! None of the park brakes built into or added on a rear caliper will serve as an emergency brake. If your state doesn't have an inspection that checks for emergency brakes, carry a pair of chocks for those situations you might need a park brake. That's what I do in my Jag rear end car (couldn't use the stock Jag park brake setup -- plus it's an auto) and my Jeep pickup (stick shift, but the park brake cables are froze -- came from up north, might fix them one day, I haven't had it long). Sometimes you need that added safe feeling that the vehicle won't move on you, like when jacking. That's why I like the metal chocks I have, can use them on a front wheel if jacking the rear up.
