I started with my 750 oil leak fix, and am now into the "since you have it out of the frame" stage.
Most members have advised to go with the OEM gaskets. Their are plenty of small "details"
you may want to consider, especially if you get down to the rings. (relap valves, ring size, honing, circlips,install techniques..on and on)
I just beadblasted and repainted mine and they look GREAT. There are many posts on this subject, just search. The big thing I have learned, is that if you do bead blast, make sure you THOUROGHLY clean out all cavities and oil passages. I though I did a good job, but desided to give it one more going over and found enough sand in a few ports to KILL my cam.
If you have no transmission problems, getting into the cases may be agressive / expensive / time consuming. I have been advised that a properly maintained bottom end should be good for 60,000+. My buddy has 62000 on his, no problems. I see yours is a 500/550, I know the 500's had some shortcomings in the clutch department.
Here are some good links, and the links to my posts.
http://www.westernhillshondayamaha.com/fiche_select.asp get part numbers, these guys match the prices from service honda.
http://www.servicehonda.com/parts.php get the best price.
http://forums.sohc4.net/index.php?topic=32081.msg330949#msg330949http://forums.sohc4.net/index.php?topic=29364.0good luck, have fun, stock the fridge....