i have a 72" i believe g series ( the first one they made). is there a way i can open it up and swap out to a muc more powerful led? im sure technology has far surpassed what was in there

i think the general consensus will be dont bother.

i think the first generation used rebels, although not the best, they are still good.

The last generation used Rebels. G and H models used Luxeon IIIs. I4's used K2s. Replacing the LEDs will require a lot of effort. The LEDs are on strip pcbs, so anything you replace them with will be mounted on individual stars. The mounting portion won't be too bad, but wiring everything the same way will be a chore.

evil ur knowledge never ceases to amaze me. what kindof wattage/par differences could i expect? any idea about the optics they used?

Wattage shouldn't change any. Output certainly will though. The change will depend on what LEDs you end up using.

Stock optics on those fixtures was about 40 degrees (Fraen I believe). Depending on the tank this is going over and the LEDs you decide on using, something wider may be of benefit.

looking to put it over a 30" deep tank. what top of the line bulb would u recommend i use if i did go this way cree xp-g r5??? , mc-e or do i have to use something from luxeon?

You can use anything you want. XP-G whites and XP-E royals would work well for a tank that deep. 40 degree optics are about your only choice for this one, but they should work pretty well on this setup.