What's the mileage on the motor? If it's 150,000-200,000 or getting there, I'd say it's overdue for the rocker/pushrod clatter, and having the engine out is a GREAT time to pull off the valve covers and get in there to replace the rocker assemblies and pushrods, not to mention the valve stem seals. They aren't cheap, rocker assemblies are ~$80 each from our forum vendor Tousley Ford (you'll need two), plus a few bucks for each pushrod (you'll need 12). It's worth it if it saves your lifters though. Those are expensive beyond belief. You'll wind up replacing the upper/lower intake gaskets doing this as well, which is also a good thing to do.
If you have the money, you could replace the heads (~$200/ea complete, $150/ea bare) with the stronger/better flowing aftermarket versions, and of course the head gaskets in the process.
You might also consider a timing chain/gear/tensioner/guide replacement. The aftermarket kits are not expensive at all, and it'd be a snap to do with the engine out. They do seem to last 300,000 miles and beyond, but it's just something I'd consider replacing at super high mileage.
The freeze plug suggestion is good too, you could flush out the block and have a really clean cooling system. Stuck-in original factory freeze plugs are pretty strong, though.
Either way definitely paint the block, either just sand/brush and recoat it factory grey, or whatever suits your taste. Just be sure to do a very light coat or two, thick paint on the outside of an engine doesn't help it.
I would also suggest cleaning up the frame and painting it and any other rusty parts in there. They may not stay pretty, but cleaning the dark corners where rust builds up and eats away at the body will make it last a lot longer.