I was thinking of running a top loader in my 544 but I am having a hard time finding one. I did find two but the are 3 speed O/D's that came out of a truck. Can you change the gears to make it like a straight 4 speeed. Can you buy the gears?
No, you can't just change the gears on them. The cluster gear is different, 4th gear (which is part of the input shaft) is also different. I'm not sure about the mainshaft, but I doubt it's the same.
It's probably time to start shopping around if you don't want to run that tranny as-is.
I've rebuilt several toploaders, and they are a pain. You've got to have special pullers that will reach around the input and output shafts to remove the front and rear main bearings, and the internal shift linkage is a puzzle if you aren't use to it.
Dan Williams Toploaders is a great place to find parts.
Dan used to be THE man in the toploader business, but is now in semi-retirement. He still sells the rebuild kits (which come with excellent instructions) along with the other stuff on his website. He set up David Kee in the business (I think he's s relative) and Kee sells trannies ready to go. Kee sells the same parts as well... at a slightly higher price. Here's his website. It also has a lot of good info.