67 MC but brakes feel spongy

[ratty65]

Ok so after replacing all the wheel cylinders and basically all the brake lines on my 65 we bled the brakes and lo and behold the MC goes bad as well. So, we replaced the MC, mind you it was not stock. After looking through tons of parts books and opening alot of MC at the parts store we finally figured out it had been swapped with a 67 all drum manual model. So we replaced the MC and re-bled and adjusted all the brakes and it seems like the brakes still don't grab the greatest. Is there any modifications needed to the MC or what kind of adjustments need to be made to the prop valve if any? I did some reading but still a little in te dark and was wondering if I could get some help from someone with some experience or knowledge on this issue.