If it's leaking between the cylinder head and the timing chain cover, then you should be able to pull the cover and reseal it with black RTV without removing the head. You'll want a copy of the Factory Service Manual, do you have one yet?
Here's a 22RE head gasket:
The oblong cutout on the far right goes to the front of the motor - that's where your timing chain sits and where oil returns to the oil pan. It's not under the same pressures as the cylinder walls, so RTV or Permatex Right Stuff should hold it. Here's the kicker - it is still technically part of the head gasket, and if that portion has deteriorated enough to cause a leak between the head and the timing cover, the rest of the gasket might not be far behind? Or maybe you'll get lucky and it's just the head bolt that sits under the cam gear is loose?
I don't know about your rattle - every time I've heard timing chain noise, it's been at idle or low RPM and sounds for all the world like a diesel motor. I'm not a mechanic, but if I was getting a fast tap or knock at high RPM, I'd be more inclined to look at crank bearings? If you're going to reseal the timing chain cover without pulling the head, you'll want to drop the oil pan anyway, so check the main and rod bearings for spec while you've got it torn apart. The other thing it could be that's easy to check for is valve tap - 22RE valves are tricky to get right, at least for me, but if you've got a rattle/knock that loud, it ought to be obvious when you check the clearances. The thing it could be that I don't know an easy way to check for is piston slap or loose wrists between the piston heads and rods. Leave that for last

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OR - just tear the whole thing down. Pull the head, pull the pan, do the timing stuff, everything. Between this leak and your mystery knock, I think that motor's been rode hard and put away wet. Might be time for a rebuild, or at least a complete check-up top to bottom. How's your compression?
Anyway, just some ideas. I meant it when I said I'm not a mechanic so I could just be borrowing trouble for you, but at this point I dunno that I'd trust your motor.