$600 would be ok if you had to do nothing to it but just drop it in. So with that said, if you have no way of hearing it run or see a compression test like Martin says, it is only worth core value IMHO
Have seen of recently many inflated used 235 parts on craigslist and ebay. One of my favorites is a shirfter top off a sm420 that looks like it has been outside forty years and completely rusted over but the seller wanted $75 for it. Make the wrong purchase and you may have to put another $1500 into it to get it up and running. Machine work aint cheap.


1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
In the DITY Gallery
Video of the 261 running

1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration