1965 dodge dart master cylinder

I haven't heard of that. First, refresh the brake fluid, which you should do every 2 years so in OH (unless you use DOT 5 silicone). Glycol absorbs water, greatly lowering the boiling point, plus rusts the internals.

Post a photo of your exhaust manifold or headers. You can find info here. I recall most use factory 273 exhaust on a 318, though it restricts flow. A power brake booster & cylinder would sit much higher, which might help.