Thanks for everyone's comments. Williwoods, I appreciate your thoughts on this too. Personally, I think this will be fine. If you look in the <1997 forum, I posted some pics of my brand new 1995 Manitou HT that I am happily riding & racing. Yes, there are risks in cracks (as with any bike really) but a catasrophic break where my life is at risk, very unlikely in my opinion. Its not like I am not racing this downhill or 4x.
I mentioned my 95 frame above because when I compared the head tube of the 1994 to the 1995, I found big differences. The 1994 was was tapered out where the headset cups are pressed in. This taper was also outside of supportive welds around the top and downtube (main problem area). My 1995 frame did not have this taper and the head tube was much thicker (sorry I did not mic the difference). By 1995, Manitou was very aware of the problems with cracking headtubes so I beleive my 95 thicker head tube was an attempt to improve this area. Also, the 1994 taper appeared to not be professionally machined (by the factory). I also noticed that the ID was not the same at the lip as it was ~3-4mm below the lip. This is a big problem if you think about it, especially if the tubing is thin. So, my thoughts on welding in headset reducers would provide parallel surface for the headset, more metal in a weak area, and the insert would be near the supportive welds of the top and downtubes. If this logic works, great. If not, then we are back to the same problems it had before. Since this frame is painted, it could always be repaired and touched up.
As far as posting a warning risk on my listing, I don't think it is necessary. I am not stating that this frame has a warrenty nor do I imply that it will not crack. I planned on building this for me as a vintage race bike and using it myself. This was the plan until I found the 95. If someone wants to ride/race it, they are assuming their own risks and by reading the listing, they can see that I am not hiding anything. They will have to assume any risks. If a person wants to buy it for display, it would be great for that too.
I must say that it was a fun project and I am very proud of it. If it does not meet my reserve price, that is fine. I can always just hang it on the wall and admire it. I will probably just relist it with a set "buy it now" price and set it for automatic renewal. If it sells, great. If not, that's cool too.
Thanks again for everyone's comments. I really appreciate it.
Cheers!
Chris