Sorry man can't help you. But your best bet is to find a wrecking yard with a 55-59 school bus or a Miltiary six by six of the same vintage.
Also there are a few military web sites that sell rebuilt long blocks. I found one a few months ago for $1800.00 rebuilt barb to oil pan.
Call Steve @ Buffalo Enterprizes in Arlington WA. (360)652-7684.
He's very knowledgable & has built a bunch of engines & has some trans. adapters & other stuff too.
Here are a few pics of my 302 Jimmy/4-speed setup.