Stock toy rears move the axle forward 2" because they are only 20.5" on the front half where as a stock toyota front spring is 22.5". But you have to add a few leaves to the pack to make them stiff enough to hold up the front of the truck.
89-95 rears are 51", 80-88 is 48"
20.5 on the 79-88's 2" shorter than stock front half
21.5 on the 89-95's 1" shorter than stock front half
Depending on where the hanger is now it may move the axle a lot more
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Also according to 4RnrRick over on Pirate the 1st gen rears (79-83) are 21.125" front to center and 48" overall.
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