Brake Valve on the side sub frame for a 69 camaro

[m22mike]

Sam and Eddie
If I may correct your nomenclature just a bit.
The round valve under the master cylinder is the "hold of valve" It holds off the front disc brakes untill around 40 psi. and allows the rear brakes to come in first to prevent nose dive.
The other valve on the frame is the rear brake pressue regulating valve.
Keep in mind Sam that all the companies out there selling these two valve's have no idea what there called. Like the link you posted.
Both these valves have been discussed at length over at CGR, and explained by John Z in detail.
Now...carry on