Need to change my cylinder head gasket set. Can i loosen the the timing belt and slip it off the cam without taking it off the crank, or does it all need to come off? Thanks for any info you can share.

 

Sounds like he hasn't done all the bolts up on the manifold, this has happened to me when i got someone to change my gasket on my car, he snapped a manifold bolt were they were really rusty, so the car sounded noisey were it was blowing.
Where the car is over heating you need to make sure that he has bled the water properly & there is no air locks, he might of done a good job with the head gasket but not with the water, this has happened also with me, I had a little bleed screw on the radiator which I slightly turned till the water came out of there, Get someone else to have a check over as if you do have an air lock it will ruin the gasket again! Good Luck!
if all is ok & still over heats it has probably a cracked head : (