First step would be to ID what axles are currently under the truck. The gearing may not that bad, especially if they came from a later truck. Now, if you really want to convert it back to a 2wd, especially with towing in mind, a late odel 1/2 or 3/4 ton axle in the rear and either a 1/2 ton I beam w/disk conversion or perhaps a crossmemeber from a later 3/4 ton ifs 2wd might be a beter choice. Nothing against the Mustang 2 based suspension kits, but they are better suited to cruisers, not trucks that still are used for hauling/towing.
One advantage that a 4x4 would have over a 2wd, though, is Low Range. Could come in handy, specially when pulling your boat out of the water. You can lock it down in Low Range, and have an extra strong pulling gear to ease it out. Plus the extra traction of 4 wheel drive.
