Yeah. radiator caps tend to need replacing every few years, depending on whether they hold pressure or not(I also sometimes see crud get stuck into the rubber seal, which prevents it from sealing).
Make sure to get a lever-lock type. *so* much better than the non-lever style.
Return lines - Not a big deal; just get a cheap $25 kit on Ebay. When installing the O-rings, use some High-temp wheel bearing grease on the O-rings and inside of caps.
http://www.ebay.com/itm/7-3-IDI-For...m1ec10da078:m:mo99yc-qj2auqcFLKKuuHEA&vxp=mtr
(Note - there's two styles of return line kits out there, one with 3/16" lines(early style) and one with 1/4" lines(late style). Either will work on any truck. It's only personal preference or matching what you already have. I think the 1/4" late-style are perhaps a little easier to work with, as there are more barbs on the hose-barb ends).
As long as you use the grease as I recommended(and not something stupid like Vasoline), even a cheap kit like that will work perfectly well. If you *don't* use said grease, you will have trouble. Period.
Injection pump wise... Make sure it's leaking from the injection pump itself and not the fuel inlet line right at the back. There is an olive seal inside that connector, which when it leaks will drip down the bottom of the pump and make it look like a pump internal seal is leaking.
Also, if it's just a single seal that's leaking on you on the pump(like the driver's side light-load advance piston), you can easily get a $30 re-seal kit off ebay. Obviously, if you take the pump apart, you have a chance of ruining something, but it can be done(and if it's just an external seal like the light-load piston, it's a lot easier to fix).
If you need to buy a new pump, idiperformance.com. Much better quality than the crummy rebuilds at the autoparts stores.