1981 and up Measures 28-1/4" between eyes and 2" wide.
1980 Measures 25" between eyes
With that old a cart finding a direct replacement multi leaf spring will be hard to find. I would measure existing spring width and length and go to auto parts store or better yet a spring shop and get ( additional leafs ) that you can stack onto existing main leaf to give you the lift and strength you need. You would need to get longer "U" bolts, longer center bolt and get clamps to hold leafs from twisting.If you can find a spring shop they could also re-arch your existing leaf for better lift and weight holding.
i heard that you can use a 25 1/4" between eyes and 1-3/4" wide trailer spring
i have never tried it
http://www.easternmarine.com/25-1-4-...leaves-us-1018