what is the visable difference between a 305 and 350. i found and engine with tranny for $500 good deal?

 

other than running the casting #'s or pulling a head to check the bore, visually they are the same.

 

Yup. Different year blocks sometimes had the dicplacement cast into it somewhere, for example most later model blocks have a 5.0 or 5.7 cast into it on the bellhousing flange behind the intake. Some others have a displacement in CI on the lower part of the block above the pan rail.
If you can get the casting numbers, go to www.nastyz28.com or www.mortec.com to look them up.