I've done a similar concept. took a 1947 ford 2.5 ton former well drilling truck, shortened the frame 2-1/2 feet and installed a 84x102 aluminum flatbed on it. front end I used a M2 kit with the matching lug pattern to the rear out of a 66 ford. that one has a 347 stroker with an AOD trans. 85mph+ is no problem. cruises like a modern truck, and has A/C!!!!. did the same for a 1950 ford F-5.
as for a market, I have not tried to sell these two particular trucks. although, without labor I have $23,000 in the '47 and $18,000 in the '50. so figure you would have to ask upwords of that.
currently I'm building a 1952 chevy for resale. was a 3600 stock which I am turning into a 1/2 ton with M2 front, S-10 rear, 305sbc, 200r4 trans and all modern upgrades minus A/C. Figure I will need to get about $20,000 for it when i'm done to make anything.
but it all depends on the quality of the build and what you have/want to put in it. you know $800 for base/clear paint or $150 for single stage enamel.
in street rod type vehicles I've found in my shop the customer gets what he wants to pay for and they have a budget. so while most like my personal vehicles, the cost is out of their range they are usually of the more budget minded.
in summery, building what is called a spec vehicle to sell, can be risky as street rod buyers all have different desires. feel free to ask questions, good luck.
daren
ps doing all the build yourself?