Here is a short explanation by Bill Hanlon on the Safari site about the GMC 55'-59' V8's. (Look at the "GMC/Pontiac V8" section on this page).
http://www.pontiacsafari.com/L1EarlyV8Pontiacs/V8%20Engines/index.html

My take is that if you can't find the engine serial number that starts with "336" as illustrated here:
http://chevy.oldcarmanualproject.com/gmc/5559mm/5559mm0i05.html
and your block casting number is not "528456" (the Pontiac block used for the 58' GMC 336 or "532000" (the Pontiac block used for the 59' GMC 336) you do not have a GMC 336 engine. I do not know if any early 60' "536387" blocks were used for late GMC 59' 336 engines.

Please remember that any of the 55'-59' V8's produced by Pontiac or GMC could have been easily dropped into your truck in the last 50 some years. I still personally think you have a Pontiac 57' 347 for the reasons in my previous post.

For more informed opinions than mine I would suggest you register at this site http://www.oldgmctrucks.com/
and post your engine ID question there. Photos of your engine and its numbers would be helpful.

I believe the above mentioned Bill Hanlon is a member there and bigbadswingdaddy is there also. There are simply more people there interested in GMC engines. Good luck with your project.



"Nothing astonishes men so much as common sense and plain dealing." - Ralph Waldo Emerson