[JLMounce]

Having just done a wilwood swap from an underperforming power booster setup myself, I recommend manual brakes.

Here's the problem with hydroboost in my opinion. The systems are largely a copy of what can be found on late 80's through earl 90's GM vans and some ford stuff like the mustangs of the late 90's and early 2000's. Those cars were designed with hydroboost in mind. In general they had power steering systems that were designed with the capacity to meet the flow and pressure demands of the hydroboost and calipers sized to counteract the incredible pressure the hydroboost sends to them.

In practice with these muscle cars, they tend to get put in front of a power steering pump that can't handle the brakes and the steering at the same time. They are also typically used in front of calipers that have very large pistons. This is why in a typical power boost setup on a GM muscle car, you see the use of the 1 1/8th" bore master cylinder, or even larger if available. You're trying to kill as much input pressure as possible in order to reduce the output pressure to the calipers. The problem with that approach is the fact that the larger bore master pushes a lot more fluid volume and the hydroboost is still creating a lot of line pressure. You end up with a very immediate "On/Off" brake pedal. There is typically very little feel in the brake pedal and because of the on/off nature of the brakes, there's very little in the way of modulation.

It makes performance driving terrible, if not almost impossible. Heck, it can make stop and go traffic terrible.

Going to a properly sized manual brake setup solves those issues, at the expense of a harder pedal. Not hard in a bad way however. It's not like the pedal you get when the brake booster isn't working. Needlessly hard without any stopping. It's a harder pedal that continues to travel, is actively stopping the car and is providing feedback to your foot on what the tires are doing.

If you're dedicated to doing the hydroboost, I would source your parts independently instead of buying a kit.

The Astro van's hydroboost I believe retains the bendix bolt pattern and should bolt right up to your 70GTO firewall. Take some length of hose and take measurements for your pressure and return lines and have them made by a local tractor company that does hydraulic lines. Or you can buy line kits too if that's more your speed.

You should address your pump at the same time. The original P Series saginaw pump is hard pressed to cut the muster for flow. It can't really run both the brakes and the steering at the same time. You'll want to go to somebody like Lee Power Steering that can build you a pump to handle the extra load on the system. Because you now have extra work the fluid has to do, you should also consider a power steering cooler while you're plumbing your lines. If you aerate your power steering fluid due to heat, you lose your brakes.

To retain a decent pedal, when purchasing your Wilwood kit, you may want to look at the calipers that have the smaller pistons in them. This may mean ordering direct from Wilwood. Their caliper offerings in kit form from places like Summit and Jegs usually err on the side of being the large piston versions that conform more naturally to the factory manual or brake booster setups in these cars.