If you have a factory service manual that'll tell you how to take off and put on the cylinder heads for your engine. There's really nothing to it, except retorqing the bolts in the proper sequence when putting them back on.
Do a search on the web, or do one on Ebay and you should be able to find one. They make reproductions so finding one shouldn't be too bad. You can also place a thread in "Parts Wanted" to see if someone might have one to sell.
72 buick shop manual i obtained my shop manual (factory service manual) and the body by fisher for my 72 gs , in 2000/09 , from -- Douglas Vogel 4779 Meadowlark Ln. P O Box 335 Dexter Mich 48130-0335 dvogelauto@aol.com