If you are down South and run on nice red clay oval tracks every week you can set your chassis up for wider front tires.
 If you are racing on a National level and travel the Country on different race tracks each week with slight right hand turns you will have a difficult time with wide tires up front. The small front tires seem to get the job done just fine especially with our min weight.  

I talked to Julian, he says $7-8000 for something like that engine. There are always upgrades, with that the price can go up.

Vanguard is the way to go in more ways then one.
not sure if I should mention anything but there is a guy near me that does a lot of testing and R&D for Honda. From what I hear the honda twin isn't exactly awesome for racing (besides the lack of aftermarket support), they have oiling problems and so on when put to the test.

The first thing I would do on an ungoverned engine is get yourself a billet flywheel.
If you are looking for some go fast for cheap ideas here you go,
 
-Mill the heads about .040" because since it is a 15hp twin it will be an early model with the thin head gasket already. The intake will still bolt on easily.
 -Retard the camshaft one tooth, that will give you another usable 500rpm or so
 -Offset the flywheel key about half way to advance the ignition timing.
 -Get yourself some good valve springs and retainers, set the seat pressure about 40lbs
-Tighten up the valve lash to .003"
-Build a nice 2 into 1 header.
 -A carb from an 18hp engine will have a larger venturi, make a nice velocity stack and install a free breathing air filter.
 -5w30 synthetic oil,
 -Clean up the ports and you are off to the races.

When you want to go real fast give me a call 

What is the engine in?

Yup,  All you need is some Ryker Racing cylinder heads and you can do it too.  

The mag side journals are different sizes, late and new model but the pto side are all the same bearing. Under normal conditions you would probably never have to replace one. Where are the side covers cracking? , I've never broke or cracked one..............except on engines that broke at elevendy million rpm but that also turns billet rods into thick dust lol.

George, will these home built frames be allowed to run at the All American?