$100 for TWO axles already geared to "better than what you're at right now" and an afternoon's worth of work to swap em in seems pretty smart to me....the new gears (if/when you get them) will go right in, and didn't you say you were changing you're layaway order from gears to a slip yoke anyways? ......does this mean you're going back to buying gears now?
Or are you gonna try to get gears, have them installed, buy a slip yoke, and source a driveline (with all new U-joints and a double cardan) all within "the next few months?".....
Ambitious man....I hope you can pull it off..... if ya do... and need help with the install lemme know.