I also have been wondering whether the rules allow a triple in the bigger classes, which  it appears they do, as you say, but 800 cc would be a bit low powered perhaps?  Good starting point though, pity I haven't any money to kick into such a project, unless there could be what I believe is called these days " crowd funding" which might bring together like minded people, preferably with deep pockets!
anyway,  good luck,
Dave