Are the heads, block, and head gaskets all original? Maybe the stock pushrods will work after all. It sounds like the length you added was just enough to hang some valves open a tiny bit.
When you say the rockers were loose with original pushrods, were they flopping around, able to move the pushrods up and down, or do you mean you were able to push down on the rocker arm and it was “springy” on the pushrod side? You will be able to easily compress some of the lifters, so it’s easy to get a false measurement that is too long. Easy to see with intake off, but more just feeling it when intake is on.
