Bore and stroke on a 352 is 4" X 3.50" and the 390 is 4.05 X 3.78". If your stroke measurement is accurate, it sounds like you have a 352. The 90 degree oil filter adaptor is a carry over from the 61-63 Birds and was needed for the full sized filter to clear the fender wells.

Ok now that your disappointed about having a 352, here's the good news. The 352 blocks had plenty of meat in the cylinder walls (according to one sourse some of the left over 352 blocks were actually bored to 4.130 at the factory to produce the first 428s). They will safely take an overbore of .050 (standard 390). Add the crank rods and pistons from a 390 and you have one. The only thing to look out for is if the engine has a 352 pan. some of the 352 pans have a baffel that will hit the crank, it either needs to be trimmed, or a 390 pan installed.