-Enchanting 4 peices to  each is 100 damage absorption, not 200. You should get a Legendary Anor Helmet and enchant it to . It's not uber expensive. Also, consider linking it with Wit because it gives much more resistance than WIS.
-If you can't afford to have INT/REC/LUC, just do INT/REC. Forget LUC.
-I agree with Chewie that you should put Vigor lapis into your dread neckalce for now. Not for Diversion, but for potential motive, mana slug (I think mages get that right?), etc.
-What type of weapon do you have? Just curious. I'd use a Rage of the Sun if I were you. I saw some pretty nice ones in Etain's AH *coughCHEWIE
cough* for under 2bill. Link with Assault 5, Mystic 5, Dual Mystic w/ REC, Dual Safe w/ maximum attack power (VERY cheap), and 2 other things to your liking.
-Oh, and as suggested previously...don't use WIS lapis. Get resistance other ways. You should have enough for accuracy from prayer unless you're soloing and in SC I don't think you have anything to worry about (white mobs are easy to hit). Find other cheap lapis to use if you want, or save a slot for slightly less cheap ones.
-Your gear is linked with Fortune...just take them out. Really, you don't have the stat points for a LUC build.
-I back up Althamus' suggestion to try a priest (instead of defender). It's also the best class for farming, especially if you need the money.
REC priests are fine to heal most people in Stigma, KI, etc. and be UM for KI because people won't take you if you are HM (no EB 3). Your mage could also get all REC/defense from gear (no INT) and you could share gear with the priest.
-I'm only level 67 and I've been farming OI since at least level 63 as the tank and only DPS (duo with a priest) and I have gear not much better than yours...however...I've been playing much less and a friend is borrowing my gear. The gear I used the LAST time I farmed OI sucked (I had a legendary anor helmet and dreamy medicus pants both nicely linked enchanted to , but my other 3 pieces weren't enchanted and 1 wasn't linked. Legend ophiston, heroic wilarin, and heroic sephiroth. I had 50 total damage absorption, and significantly less REC than you), and I still did fine with a level 56 HM priest healing me. I think you could do it. Have you tried? I can go with even low level priests (like, under 55) and be fine but if you want go ahead and see if a level 70 priest will go with you. You're level 70, so I'm sure someone would try. Maybe ask a guildie. Don't sell yourself short without trying. You have more defense than me (when you gave your stats, that's without Body Protector, right?) so I don't see why you couldn't tank just fine. Just make sure you have ele skin, body protector, prayer, an AOP at all times and you'll be good.
BTW, nice stats Chewie...