Yes, you'll need the flange adapter from either an aerostar or ranger w/ an 8.8 rear axle.
You'll also need new spring perches, u-bolts, spring plates, and shock mounts. You'll probably want some wheel spacers too because the axle is a little narrower than stock.
You can still do this all within your remaining budget and you'll get disc brakes, a beefy axle, and potentially a limited slip. Depending on what gear ratio you're running now they come available w/ 3.55, 3.73, or 4.10 stock. The 3.73 ones seem to be the most common to also have a limited slip, but if you're crafty at the junkyard you can do a quick carrier swap if the ratio you want isn't available with one. There is no carrier break on the 8.8, but on 4.56 or numerically higher you'll either need a special cross pin or you'll have to grind a few teeth down a bit to get a stock cross pin back in.
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