Where to start trouble shooting power brake issue (72)

[Ekliptix]

After the 350 to 402 engine swap in my 72 C10, I've found the brakes are not very effective. The pedel is stiff, but it takes all my power just to stop the truck. So, I have not been driving it out of safety concerns.

Things I've tried:

• Added a vacuum reservoir. No difference.
• Bleed the brakes. No difference.

What other things can I check? I'm not very familiar with the mechanics of the power brake system, so maybe a diaphragm or something.

Thanks for any input. I'd like to get it on the road, without bringing it to a mechanic if possible.