I am having the head on my 86CJ7 258 rebuilt. I am thinking when I put it back on I might as well bolt on a header.

What kind of performance increase on a stock 258 will I get? The only mod I have done to the engine is a MC2100 carb. At what RPM will I see the improvements?

Will the header bolt up directly to the existing exhaust?

I ran the 258 for a while and used the Headman dual outlet headder for dual exhaust. It did bolt up easily but the performance gains for me were in the upper RPM. If you are climbing sand dunes it would be great. If your into the rock crawling I would look into the single outlet and single exhaust for a little more lowend torque.

Just a question, but if you are thinking of going to a header anyway, why didn't you go to the 4.0 head? There's a pretty substantial power increase...

Will my intake manifold, valve cover, etc work with the 4.0 head?

The intake manifold will work fine, you can get the valve cover off of the donor 4.0... There are a bunch of write ups on the web about it... they say it can add up to 40hp...

here's one (http://monsterslayer.com/jeep/40Head/40Head.htm)

It is a little more work... but the benefits are great!