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A lot of what is in this thread is common to many rebuilds, however some things are a little different when you thinking of a race application for a T boat.

Used Parts
People who don't know me wonder why I have some many engine parts. It's the cost factor. It is too costly for marinas to repair and rebuild old motors. They usually sell the gear case and power trim. Then dump the rest. They only offer the owner a few hundred for the complete motor. Common parts wear out, so there can be multiple motors with the same problem. You learn what the common problems are. Number one is oil injection failure and that generally ruins the crank which is costly. Number 2 is gear case normally caused by no maintenance. The secret is to ask the seller what is wrong with it and then go and see it. It doesn't take long to check one out. Certain motors like a Yamaha Pro 50 are popular because the have a great power trim unit and common parts. So decide what motor you want and be patient. You can get one for $100.00 to $500.00. I have very few dollars invested in old motors and I have got hundreds of dollars worth of excellent parts from these motors.

Crank Shafts
New cranks cost between $700.00 and $1200.00. A used crank if it is not damaged is just as good a a new crank. A repaired crank for a race application is not the way to go. Many cranks are modular. Example the Yamaha and Tohatsu. You can make one good crank out of a few used cranks. That refers back to the above about getting parts. Cost effective.
4 Spline OMC 3 cylinder cranks are getting harder to find. The broken non oil injection power heads have a better chance of a good crank.

Pistons and bearings
In T you can run after market pistons. In most cases they are equal or better than the stock replacement. A wisco piston expands more than a cast piston especially in an OMC. Don't make it too tight in the bore. Use new bearings.

Reeds
Boyesen or similar reeds are a must.

Oil injection
You don't want it.

Fuel
Premium Shell and a good oil.

RPM
These stock motors can run all day long at 6000 to 7000 rpm.
Your not hurting them.