I cant give an estimate,but the car looks real nice,and will probably not be cheap!...a friend of mine sold his '57 Belair he had since the 70's for 18K a few years ago,and it was not a perfect example,it had some rot repair and a so-so paint job,and a non original built 350 V8 in it...shows what a car like that here can sell for,just because there aren't any left to choose from really ..
Looks like a 235 straight six,and someone evidently adapted an HEI distributor to it somehow?...those engines are very torquey,I had one in a '56 Chevy pickup,everyone who rode in it was surprised to see a straight six under the hood--they all assumed it was a V8 because you could lug it down to 10 mph in third and step on the gas,and it would take right off,with no bucking or pinging...the "Blue Flame" 235 was used in the '53 Corvette too...too many people rip out the original six and put a V8 in the old chevys..its only original once!..