help hard break pedal weak breaks after swap

I,ve also had brake issues in my 68 Barracuda.I went through the whole system and everything is fine.I put a vacuum tester on my booster,had 20lbs in neutral,put in gear and it dropped to 15lbs.I still had a hard peddle and minimal stopping power.I took the booster off(rare 7 inch)and took it to Brake speacialist last week.I think it,s like $380 to rebuild,but would sell me a 9inch with M.C for $370?WTF?I called today,they still haven,t looked at it.Good luck.