To be honest, I have built 6 STX38's, two had twins....they don't like to handle at high speeds. I would move up to the L100 series John Deere or the older 160-180's.
I had to run and angle iron all the way up and down the hat centers on the underside, and then fabricate a cage to hold the tranny. This left little room for the drive system. Plus, its a stamped steel frame - one piece, if you screw something up,(Big Wreck) there is no fixing without major work. They make great IMOW or J/P, sometimes decent GP's if you can get it to handle - but again, a one piece stamped steel frame is bad news. I started to run into stress cracks on the fender deck all over the place. Also the wheel base is tad bit short. And then the hood....when you break that, its over $300.00 new, and very hard to find one used. I would move on.