Nah, it happens to all of us. I don't think I could figure out half of the new headset and bottom bracket standards which is why I am so familiar with the Park website.
Can't wait to see the progress on your new frame. My 1990 M800 is also an April mfg. date:
51804901810
Your frame is made for a 1" steerer. The 1" number refers to the OD of the steerer tube. Headsets (and tires, and bottom brackets, and every other part that has ever changing standards) can get confusing. When I get lost I find that Park Tool has a lot of useful info on their website. The...
I think it is a 1990, it was the only year with round chainstays and cantilevered dropouts. Probably a late 1990 (August +/-) with the decal on the downtube or it could be a euro spec thing. I would love to see the serial number on it.
There are kit to convert from Headshok forks to conventional forks, which is what is fitted to your bike. Post a picture of the serial number, that will help fill in the details.