Help in removing/altering the yoke from a drive line.

Hey folks, hope all is well in CTOA land. I need a few pointers in removing the key from a drive line yoke on my old Oliver hay rake. The story is this: I was raking up some mowing remnants to use as bedding when the yoke at the drive-side u-joint (it's a ground driven rake) broke. Since the rake is as old as dirt, exact replacement parts were out of the question. I found a replacement yoke at a local drive line outfit, but it's a tad longer/bigger than the original. Therefore I need to shorten the mate to the replaced side. The yoke that needs shortening is attached to its driveline with a rectangular key. I've never done this before, so I'm wondering how to remove that key. And curiously, I don't see a matching key-notch in the shaft itself. Does that mean the key is tapered and the only thing holding the shaft on is the force of the key against the yoke and the shaft? Anyway, before I can move forward the key has to come out. Help!