bad noises coming from an 87 4.0

So far its got worse and worse and when it started it was only when the motor was cold but, I have a really bad ticking noise coming from my engine. I wouldn't call it a knock, but its kind of a tick tick tick that goes a way for a few seconds and then comes back and is getting much more frequent to the point its almost constant now. I am thinking its probably bad lifters and from what I'm told chances are if the lifters are bad the cam is probably shot too. The other thing that worries me is that if my oil pressure gauge is right my oil pressure is only 22 PSI (I have a Canadian model and all the gauges are in metric so my Oil pressure is in Bars, its usually right around the half way mark between 3 bars and the gauge goes up to 5.4 bars, so I figure according to my gauge I get 1.5 bars of Oil Pressure). I am not sure if this is accurate since from the sound of it all my noise is higher up in the motor than the crank. Its really possible that I could have something shot in the bottom end but wouldn't it be a lot noisier if that was the case? One thing I was looking at too is there is an 89 or so 2wd 4.0 for sale for pretty cheap that I was looking at, assuming that the engine checks out in this 89 would it be worth my while swapping it in to my 87 which has a much better body (the 89 has rot issues).

My Two Cents...

I am currently smack in the middle of fixing a similar problem. Is the noise really bad when you first start it up? Does it go away after a second, only to come back later? Also, changes in RPM will usually get it to make the sound. I thought lifters too on mine, dropped the pan though and the rods were shot. If your lucky, and your crank isn't too bad, you might be able to just slip bearings in it though. At any rate though, if your donor is cheap enough, its not really worth messing with. I drove a 4.0 4x4 donor home for $75.

Sounds to me like you do have bad lifters and it IS quite possible you'll have worn cam bearings as well. This could be the reason for low oil pressure but since your engine's old and high mileage, the chances are that the rod and main bearings are shot too.
Whatever the problem is, you'll need to rebuild the engine anyway. You could do another stock rebuild but it's also tempting to rebuild it into a stroker. Think about it.