Forget the 4 valve conversion. (if you have been lurking this comes up every 3 months or so, not as often as can I turbo my NA....... but you get the picture)
- Buy a headgasket set/water pump/rollers/belts/front seals
Pull the head. Have it rebuilt if you wish. I have seen some high mile heads and the only ones that I have ever seen being a problem are the turbo heads. The exhaust side get quite a pounding. The seats are usually worn. On your NA .......check for valve guide play/ seats......... if it looks OK. Throw in some new valve stem seals and call it a day.
- Replace the waterpump, front seals and belts and have someone check your tension.
The only places I see you getting IN real trouble if you are new to this.
1. The waterpump studs. Odds are you will break some.
2. Tensioning the belt. It would be nice if someone in your are a would help you out on this.
The rest is pretty much tear down/replace/put back together. As long as you are familiar with the torque specs, steps involved it should go ok.