on a 272  can the valley pan go on before heads , 1 head is already on  thanks Fred

Yes.
Some of us have encountered difficulty removing or installing the valley pan with both heads installed. When I removed the original valley pan with the heads installed on the 292 in my 55 Tbird, I slightly bent the edge of the pan. I was able to straighten it. I later gave it to a friend in need of one because I had purchased an ACE cast-aluminum valley pan. The Ace pan is notched to allow for easier removal and installation with the heads installed. I'm hoping that it will seal better as well. In the meantime, Daniel Jessup (hotrodreverend.com) is working with Genuine Gaskets Tennessee to produce Y-block silicone valve cover and valley pan gaskets, in addition to  their existing Y-block silicone oil-pan gasket. They also have a silicone gasket for the C4 transmission pan for those of you, like me, who are replacing the Loadomatic with a C4. 

To add to 55blacktie's post, I too have had great difficulty installing my valley pan with heads installed. This '64 292 block had .023" removed from the decks and an additional .010" from small letter G heads. I didn't have difficulty installing the valley cover until after the above machine work was done. I believe bringing the heads down and closer together due to removing metal from the decks and heads is what was responsible for the difficulty. It took almost magic to discover the right combination of movements and angles to get the valley cover in place undistorted. 

 

64F100 57FAIRLANE500

thanks black tie and supercharged ... Thats what it appeared to me  , I have one head off so the valley pan next   thanks Fred

Maybe it would be a good idea during assembly to try installing the valley cover with the heads and gaskets in place with out torquing the heads. I'm thinking of a time when the valley cover may need to be removed some day. If it can't be installed with the heads in place, a little tweaking with a Dremmel tool might do the trick. Could save a lot of grief in the future. 

64F100 57FAIRLANE500

just a couple more questions guys . In the service manual it says apply sealer to both sides of head gasket , pretty sure you dont use any sealant on new type fel pro head gaskets , and are there any intake or head bolts that go into water jackets and require sealant , I dont think so but wanted to ask   thanks Fred

No sealant is required on composite gaskets or intake or head bolts, but use a bit of oil on the threads and underneath the bolt heads.  

thanks blacktie   Fred

any tricks or tips to get that heavey head up under the hood and in place   Do you guys usually put the gasket on the head or the block ? would a light spray adhesive help or would that screw things up ?  Fred