You might want to look into which county it is presently registered in..Cherokee, Clayton, Cobb, Coweta, DeKalb, Douglas, Fayette, Forsyth, Fulton, Gwinnett, Henry, Paulding and Rockdale counties all require it to pass an emissions test before you can get tags. You might want to check what axles he has under it as well, l would think a Dana 35 might not be stout enough for the kind of torque a 350 is capable of putting out. Have a look at the driveshafts, see if they have been shortened/lengthened and what do the welds look like on the tube. Also are they in line with the pinions, or does the driveshaft angle off to one side. If the engine is carburated, the installation is relatively straight forward compared to wiring a direct injected engine, There are kits available that do a nice job of tieing in the computers etc. With a TH350 , l too would not expect to see anything other then a carburetor on top of the manifold. Nothing wrong with that, but it indicates, at least to me that the owner probably got an engine out of an old pickup, cleaned it up and installed it. Get the engine serial number and you can easilly find out year, and application it was originally used in. Look on the passenger side head, at the front. There is a machined pad, might be obscured by the alternator, that should have two sets of numbers on it. Write them both down, l can' t remember which is which, but from those numbers you can find out a lot.
How can you trust an atom, they make up everything