Just a suggestion....before you go changing a bunch of seals and chasing leaks, you might stop and ask yourself "what is causing the leaks?" The most common answer is excessive crankcase pressure, which is pushing the oil past the seals and up the distributor. An engine that is worn out or an engine that has been setting up for four years, is likely to have compression leakage past the rings, which builds up crankcase pressure with the resulting oil leaks. A quick test is to pop off the oil filler cap with the engine idling....watch for "blowby"....huffing fumes that increase dramatically when you increase your rpms.
Before I did anything more I'd run a compression test..(Do "search")..first dry and then again with a squirt or two of oil in each cylinder. If the compression pressure comes up appreciably with the oil added, you know your rings aren't seating properly, either from being "stuck" from sitting up or worn out from high mileage. At this point you can opt to run the engine for a while as-is, to see if the rings will settle in.
If the truck was running okay, no oil burning, smoking or leaks when you parked it 4 years ago, I'd say it would be worth a shot! However, if the engine was high mileage and had similar symptoms when you parked it, it may be time for a rebuild. Existing conditions are not going to get any better with age!!!! Hope this helps.
Dave
