I think the fields you have selected are good, maybe even too much. I have always been curious of how many Com-Pacs are still out there.
I use to own two Triumph Sports cars, a 59 TR-3a and a 63 TR-4. The Vintage Triumph Sports Car Club had a great registry and could look up all sorts of data on original color, equipment, options, port of entry etc. it was big help when trying to restore to original.
The biggest problem I see is incentive to register. What I find is the easier it is the more successful it is.
If we had a big notice on the home page that would help. Then perhaps we could invite people to email the info. I would be happy to take the emails and put them into a database. I would use Excel because it can be sorted any way you want.
People are funny about privacy so maybe just homeport.
The registry could be posted as an updated text file on the site?