Weaver Base for Remington Rifles - Model 7 (since 1999) & 673
# 35M (48500)... Front Base
# 421M (48444)... Rear Base
Although it is not impossible that you have a bad receiver, it is improbable. But hey, anything can happen.
I looked at one of my 673's and the front mount is more curved than the back mount, the rear mount is much thicker than the front mount, but it has to be to be level. The rear mount hangs over the ejection port, which I personally think is stupid. I also think one piece mounts should be available for these Receivers.
Greybeard is correct. Designated Weaver mounts for the Model 7, which includes the 673, is 35 (Fr) and 421(Rr).
(I originally put this reply in a different thread and it took until today to catch my mistake. Darn Alzheimers...)