Ivan has a couple posts over on the Horology Crazy blog showing how to modify Marathon divers. There's a JSAR conversion that involves swapping parts from the ISA 1198-103 and ETA 2824-2 movements. And the SAR mod involves removing the cyclops lens and changing out the date wheel. The whole process for each is laid out in an easy to follow to way. It's a great resource for anyone considering these modifications.

JSAR Conversion and SAR Modification