I have a 98 sidekick on 33" bfg's.I was going to put a header and 2" exhaust on it.What else can i do for a little more power.It's my daily driver.the motor has maybe 10k on a rebuild.

Whats your trans and gearing situation?

5 spd with 5;13.i think im going to buy the undertaker to help my gearing out.

K & N cold air filter kit works well on mine.  and all those other mods youve been told about too

I been thinking about just putting a toyota 2.7 motor in it.i just gotta find a write up if some one else has done one already.-

Get a set of the 5.63 gears and you'll notice a real difference. Your tires are killin your power. If you could find the 5.83's ( unlikely) that would be better, but they're even rarer than the 5.63's now. There are a couple of sets for sale in the Classifieds here. That would help quite a bit.

I would rather put the 1000+$ spent on used R&P's, towards a NEW "undertaker" and be able to run far stronger R&P's.

I been thinking about just putting a toyota 2.7 motor in it.i just gotta find a write up if some one else has done one already.-

I have installed a 2.7 l Suzuki V6 in my 93 2door.  It is a tight squeeze and combining the wiring systems takes wiring knowledge.   I would recommend a 2.0 or 2.3 l 4 cylinder for an easier swap for the power gained.  You can check out my build thread but I can't link to it, I am on my phone.
If you have a two door, the driveling angle may be too much with the undertaker.

Does any one sell and adapter for my sidekick tranny to a toyota 22r or toyota 2.7 motor.Im just thinking about putting a toyota motor in it.

Give Trail Tough a call, they sell a 1.6l to Toyota adapter, maybe you could hook it up in reverse.

http://www.trailtough.com/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=214&category_id=13&option=com_virtuemart&Itemid=53

In my view there isn't much reason to do a partial swap.  The 22r is 95hp, 130lb torque.  The 1.6l 8v is 85hp, 95lb torque, the 16v is 95hp, 99lb torque.  Not much of a gain for the extra weight your adding and you don't even get the advantage of running the Toyota t-case/transmission setup.  For the V6 I would want the larger transmission as well to handle the extra power, along with new axles. 

I think i should just put the toyota 2.7 4-cyl in my sidekick.

I'm surprised no one has said it but if you are willing to go to all the trouble of swapping in a totally different motor why not just install a turbo and keep your fresh motor and enjoy a nice kick in the pants power boost. Both Bentparts and I have done it with great success as well as others. Food for thought

Do they sell a bolt on kit?

I think you can buy a manifold now, but no kits I know of.

Check on ebay for the manifold, the rest is easy to piece together