I asked around the officials in impound (re Modified Sports) what constituted a "single engine" in this very context.
I was told by all but 1 that it had to have a common crankcase (or at least appear to, a single oil pan was suggested to help that appearance by more than 1 person).
No bolting 2 engines together in MS.
You will notice I didn't mention any names of officials.
I shall not, if that sort of info impacts your racing effort, you need to get it direct from the people that get to make that call.
FWIW the individual that said different was quoting the older rule about no motorcycle engines in cars and no "hand built" engines in cars (the way it was put to me it had to be a production engine, in anything but a streamliner, makes me wonder how a Keith Black qualifies :confused:).
Said individual wasn't working impound though.
I remember that rule being listed as changed on the rules page on SCTA-BNI, be interesting to see what is in print when my '11 rulebook gets here.