This is actually quite easy. I think anybody can do it. It's more or less of just finding the right parts and putting them together. While you are at it, you might as well change the oil, too.
You need 1) the oil cooler kit. I like the 2000+ style cooler better than the older style. They are all interchangable, I believe. I found a set in excellent condition on ebay for $200.
2) a set of nipples to connect the hoses to the engine. Also need the bypass spring so the oil would be redirected to the cooler.
3) the last piece took me the longest to find - the intake valve over on the horizontal cylinder. I paid $40 for a bucket of left over parts off a crashed SS. The cover was in it.
Once you got all the parts, you are now ready to bolt them on. Some might do them in different order, but this was what made sense to me.
Take off the intake valve cover and put on the new one.
Drain oil first, as if you are changing the oil. Take off the 2 bolts that caps the outlets. Be sure to save the washers. You will need need them when bolting on the nipples.
Connect the oil cooler and the hoses. You can already see your 620 transformed!
Remove the oil filter and remove the stem that connects the filter to the engine. This will take some elbow grease. I used my foot to anchor the wrench and really cranked it.
Install the bypass spring so the rubber part blocks the hole. The picture is looking up from underneath. Reinstall the filter stem. Make sure you use a torque wrench. I forgot how much to torque it... Check with your dealer on that.
Put the oil drain plug and filter back in. Add oil. let her run for a bit. Stand back and admire. *I miss my yellow 620!*
