Suzuki built a 650cc water cooled 2 stroke twin for Arctic Cat. I think
that engine is about the ultimate in big bore 2 stroke twins... At one
time I considered getting 2 of these and putting them in a small sports
car like a Triumph Spitfire but I've since moved to a state that does
emissions testing and that won't pass here...

Suzuki just about ruled the 2 stroke motorcycle market with their rock
solid reliable engines. You could count on a 75k miles out of a Suzuki
triple when the other companies' bikes would only go 15 to 20k miles on
a set of pistons...

There were also some big bore 2 stroke dirt bikes. I know all the major
players in the market built them but the one that comes to mind was a
500cc Husqvarna single. Sleeves, pistons ect are all available for
these bikes could be used to build your own. The easiest way to go is
to use someone else's engineering and machine work to build your engine.
That way the major parts to make would be the cases, barrels and
cylinder heads since the bike ones won't have adequate cooling. I
imagine that a 1000cc 2 stroke opposed twin would be pretty cool and
could be tuned to run at an RPM low enough for direct drive. However
it's not a good idea to put a prop on a built up crankshaft like all 2
strokes use and a belt drive or some such would be required.

I would highly recommend reading the 2 stroke tuners handbook if you can
find a copy. I have a PDF version but it's too big to eMail. Also talk
to Charlie at Superior Sleeve in Millwaukie, OR. Charlie has built more
custom 2 stroke engines than just about anybody alive today... If you
can catch him when he has time to talk, he will enlighten you a great
deal. It's been more than 20 years since I was building high
performance 2 stroke engines and I've forgotten a lot over the years...

Good luck and keep us posted if you go on with this project.

Tony