Brake problem on my 69 Polara

[PolaraGuy]

Hello guys... I'm new here. I'm the proud owner of a new 69 polara sedan. I was having some brake issues or at least I think I am. You see, my car has drums all the way around and since I'm quite used to having discs, I figured that it was normal to exert a little extra pressure to stop. However, I have power brakes and I'm not quite so sure it requires THAT much force to brake. I did a pressure test at the relief valve on the brake booster itself. I'm getting 16 psi with no brakes applied and only 16.5 with them applied. Is this normal? I bought an old thick Dodge Polara maintenance manual and it doesn't give me the specs on this. Any help would be appreciated...