Yes, you can remove the head from your Mach 3 Combo. Here's how to go about doing so:
Depending on the build date, your head is retained by four or six screws through the end flanges. The head will come free once these have been unscrewed and removed.
PLEASE NOTE: Do not remove the screws around the logo. This will cause some internal parts of the amp to come loose which will void the warranty.