You would need to replace the whole piston block with a used one if you are going to do that. That said, it's not worth the trouble. Used pumps are a dime a dozen..... or at least $100 for one, and you can find dozens of them.
Just get a used pump. Your 129 is manual lift, so you need a non-ported pump. Might get one of these cheaper. Put up an ad in the wanted section.
Oh, and I'm not jumping on you hard for this..... but you managed to post this in the "Welcome" section under "Forum Rules". I moved it. Please make sure you find the proper section in the future to post in.