Newbie engine questions

Ok, so firstly I officially got the '89 Laredo 4.0 5spd signed over to me today. Had a hell of a time getting the two bad wheels off of it, so since having limited tools, especially when I wasn't at home, just got a temp plate on and called CAA to do if for me. now to get the two bad tirres off. At present I've never driven shift before so it should be a fun learning expeierence. it's got over 278,000km on it, but other than having to deal with leaking oil, predominantly I think is from the vavle cover, it runs amazing. No noises, clicks, ticks, clunks or anything else. Needs a GOOD cleaning though! Couldn't pass up the great deal on it, Not sure what we're going to end up doing with it. We've talked about restoring it, but unsure if we'll do that, or just resell it after doing some work on it. We shall see.

Now to my '90 Pioneer which is my present DD. The engine has some noises which I've been always concerned about since I started driving it. Compared to the '89 mine makes a hell of a lot of noise.
I've just this past week changed my oil, and because I'm leaking oil, seeping from the head gasket I suspect, I put in 20w50 for the summer. It has helped decrease the laeking, and increased my oil pressure a wee bit as well. I hear mainly a fairly audible ticking noise, kinda of like a fast ticking clock, which I think sounds like it's coming from the lifters. I actually found MMO up here, so added that as well as it's been mentinoed by a lot of people on here.
Now, within the ticking noise, and sounds similar and the same timing, I here now and again what sounds like an even louder noise, that I guess fort of sounds like a clack, kinda of like metal on metal, then it will fade. It's loudest, or at least seems to be when at idle. When giving it gas, I think it still does it, but not as noticeable with the fan and muffler. So for the big question is, what is actually going on to cause this noise? What can I do to lessen or fix it? I am looking in the near future of having the head gasket done, so will thie help any? Should the lifters be replaced? or is there something else with the lifters that need to be repaired? I don't know much at all about engines so want to learn and undestand what is going on, and if it's harming anything.

Only other question I have, on jumping the '89 today, we had it running but I noticed that there was some grey smoke coming up aong the drivers side of the engine out by the plate I guess it is, and the fuel rail. I'm thinking this is maybe either the oil on the engine buring off, as it's been sitting since last summer pretty much, or is it exhaust coming up through a possible crack somewhere, possibly in the manifold that seems like to be prone to cracks. Anyone have ideas?

Sorry this is a bit long, but just want to be detailed as possible. Thanks for any help and suggestions anyone can give. Will be greatly appreciated!

well i'm no expert but, the clicking could be the exhaust/intake gasket leaking. this is pretty common problem on jeeps 4.0. louder clack could be a little piston slap, also possible problem that's talked about quite frequently, my engine has a little noise when idling and ' when i crawl under while idling it is very noticable. probly sounds worse than it is. my exhaust leak seems to have a much more adverse effect on it's running condition than the slight piston slap. as far as head gaskets etc. thats pretty serious for some of us and i'll let others address that issue. just my $.02 on two possibilities....

Thanks for the input. Always appreciated. I know the head gasket can be a major concern, so I've been keeping an eye on it. Nothing changed, not leaking coolant, except for by the overflow tank in the last couple days which I will be addressing. I think the tank just needs replacing as it's the original one.

Just want to know if it's something I really need to worry about or not. As for power on the '90, that's never been a problem. I know the head gasket can be serious, so have been keeping an eye on it. I'd love to be able to do it myself, but like formentioned, I don't know enough about what I'm doing, so unless someone local with the right tools can give me a hand, I'll have to take it somewhere to get done. First thing I'll do with the '89 when I get it here is degrease the engine which badly needs it, and then remove the valve cover, clean it thoroughly and put it back on. I actualy picked up a spare from the wreckers so that I can clean it and when it's ready, just switch it out. Should have it here sometime later this week. Just have to do the two tires tomorrow and put them back on.