Not the same. Pre 64 H&H magnum have .425" hole space and post 64 is .330" hole space. I have either Weaver Grand Slam, or Leupold QRW / PRW steel bases on my 375 H&H. I don't remember which brand but they are steel and do not extend over the ejection port. I have a Leupold Vari-XIII scope in 1.75-6X on it. It fits and functions just great.
