You can, I did but just because I could. My heads were different part numbers (one was not original) and the porting and head machining didn't cost me much so I went for it. You should cc the heads and figure the compression ratio you have. I don't have an idea how much of a mill gets you "X" increase in compression. I would imagine it also depends on how big the chambers are. Compression is important and you don't want it too low. The wrong cam can bleed off compression and you end up in the 7's and no bottom end power. If you mill .030 off the head surface you will want to take .028 off the intake surface of the head. Here's just one thread here on the subject. I used the search feature and typed "273 milling" to get a list.
**Milling .030 off '920 - 273 heads**
