Are you sure that it is a 352? C6 is not a four speed automatic and didn't come out until 1966. Some ones done some work to this car and the engine might not be a 352. I had a 352 and did not like the performance at all!! and me and my brother tried to. 390 much better. and you might already have one.
PULL A HEAD AND MIC THE CYLINDER.YOU HAVE TO CHECK A SHOP MANUAL BUT I THINK THE 352 HAS A 4.00 BORE AND THE 390HAS A 4.05 INCH BORE. ALL FE BLOCK HAVE 352 CASED IN THEM.