I dont want to invest an extra $150 into a G3 clone if I dont have to. I was wondering if a CETME will take the "fat" angular hand-guards and a fixed G3 style retractable stock, ala G3ZF?

I'm considering buying my first H&K clone and using it as the basis of a "stargate" rifle...

The G-3 uses a hanger system on the cocking tube, with a pin that goes threw the fat hand guard and the hanger.  On the cetme, there is a round raised sleeve (just behind the front sight on the barrel).  To us the G-3 hand guard, you will need to remove the ring on the bottom and sides, but leave it portion in between the barrel and cocking tube.  This section will keep the forearm from dancing up and down with the pin in the forearm (you will still get some movement, but a little more as if you had the hanger).  The down side is that if you attach a sling pivot to the forearm and sling up, the pin will press down on the barrel, instead of the hanger that the G-3 has attached to the cocking tube.

Bottom line is that you attach a Wide forearm; you will just need to do a little work on the forearm-retaining ring to make it work.

Here is a run down of what is interchangable:
yes on barrels, and barrel pins
no on trunnions
no on bolt carriers
no on locking pieces
no on bolt heads
no on bolt locking levers
yes of firing pin
yes on firing pin spring
yes on recoil spring
yes on buttstock housing with minor fitting
yes on buttstock with minor fitting
yes on grip frames
yes on complete trigger pack swaps
yes on rear sights when the entire sight base is swapped
yes on slim or wood handguards
yes on wide handguards with minor fitting
yes on triple frames
yes of flash hiders / muzzle brakes
yes on triple frame sling eyelet pin
yes on cocking handle, and spring
no on cocking sleeve
no on cocking tube
yes on triple frame end caps
no on recoil buffers unless you use hk buttstock housing, and hk buttstock
yes on pistol grips - slight inletting may be needed
yes on buttstock pins
no on buttpads unless you swap the stock with the pad as a set
no on hk 21 rubber buttpads unless you use the hk stock