56 Short bed on 79 Blazer Frame

[mustang51p]

I am beginning may project and am looking for advice and help. I am looking to stretch to Blazer frame to the correct wheel base to mout the bed of the truck. It looks like I need to stretch the Blazer frame 11 inches to get it to stock length. Is that correct? Secondly, is there anyone with a scrap frame that I can get the straight sections behind the cab from? I am thinking with z cuts I will need about 22 to 24 inches of frame to make a good splice. ANy help or advice would be greatly appreciated.
Thanks