Paul B ,Yes I would go AC Ace - and would be with either AC's own engine or a Bristol engine - both just under 2 litre's
MGB at 1798cc is class DP -
Sprite at 948cc is class X - presume for Tiddlers under 1 litre [ 58 cubic inches - for any American in the group - and Ken who lives there !! ]
I am guessing here - will have to do some research on the SCCA in the 1960's
Cheers Guys
and having posted this have just seen Ken's next entry !!