90 degree adapter leak

Sounds like you might have a later adapter and are putting it on an early motor. I just ran into that with my resto block. I could not use the early plate or adapter on my new block. I had to use a plate from a newer magnum block even though it was a LA style resto block. You should check the offset on both gasket surfaces. on the block and the adapter. Using a short straight edge. I have seen this problem first hand