Do you have access to an Oade passive cable? You can use that to provide a coax out without cracking the case. While I know Doug, and a few others, have taken the 7 pin dongle off SBMs and soldered a female coax connector in it's place without issues, I always believe in looking for a solution that does not involve non-reversible modifications that could have problems if not done correctly.
Oade 7 pin to coax cables are frequently sold on the YS, so you should try to grab one of them before having someone hack into the case and modifiying it for coax out, IMO.