I published an article on this in CLW and have received some feedback via private messages.  I've decided to "go public" rather answer the messages one at a time.

First of all, it isn't just the 100-miler in Toronto, September 26, 2010.  There's a whole season on racing in Ontario and Michigan.  The races are basically 5-mile (70 lap) qualifiers and 10-mile (140 lap) finals, except when low entires or time constraints lead us to have everybody in the 10 mile finals.  The biggie, the Grand Prix, is the 100-mile (1,400 lap race in Toronto.

I strongly suggest that you test the water in one of the shorter races:

May 22, Rouge Park, Detroit,
June 5, T&D, Toronto,
June 26, Beanfield Gran Prix, Dresden,
August 20, MAAC Nats, Dresden,
September 11, Rouge Park, Detroit.

There has been some quetion about the engines rules.  I grew up on the Northern Frontier on the banks of the Saint Claire River, so I'm naturally fluent in both MAAC and AMA.  So let me try to clarify the engine rules even more.

You can buy an LA 25-S and use it as is.

You can buy an LA 25 RC and change to a 22312000 Venturi 2025FS ($8.99).

If you do not chose to use the remote NVA you can replace it with 22311000 Needle Assy 2025FP ($11.49).

You can use the plastic backplate or replace it with a metal one from the FP, TT, Magnum, or pretty much any source as long as it's the same design as the plastic one.  If you push the limit on this issue, bring a legal backplate in case youn get caught.

An other changes will cause this guy to disallow your engine.  
If this happens, you will be the first offender, the original sinner.

The key element here is having an LA 25 that's just broken in to the point where it runs fast and pits quick.  Not engine modification, but proper handling of a standard unit.