Step 2: Frame reinforcement
These square frames were welded into the frame, then the end I cut off was welded to the back. The minimum height requirements for my class is 4" from the frame to the ground. So its important to know what size wheels you plan to use and where to mount the axles in order to meet that requirement. The lower you can go, the better handling the mower will be. Mine site just at 4" off the ground.
Next, I welded two lengths of square tubing along the top of the axle brackets to the front tubular frame. I did this because the transmission will go underneath. A piece of diamond plate will cover it, and above will be the seat. This will give me easy access to servicing the chain and transmission and also protect me from flying debris or potential chain failures.
I am using a right angle gearbox for this build. Why? Because the other choice is to use a 3-5 speed gearbox used as standard equipment on mowers. These work fine, but it also means you'll have to change the grease in them and perhaps invest in hardened gears since the originals will strip out much easier. With a right angle gear box, or RAGB, there's only two moving parts. Plus, they are made for higher speed applications and therefor perfectly suited for this application. More simplicity means more reliability.
Additionally, I am using a centrifugal clutch. This is a higher quality, higher HP rated unit that is heavier duty than typical go-cart clutches. The springs can be adjusted for higher or lower engagement.