Bugzyla.com sells a beam that fits the ball joint spacing but uses link arms and spindles.
With stock LG spindles 29-30 " tires are about the max the left front tiny spindle with the speedo hole can take. Get someone to magnaflux them. The ball joint spindles are stronger but cannot be easly modified for more travel. My 33x9.50 tire passed me at 50 mph when the spindle broke. Nanco has some aggresive 700 15 tires as does Yokohama.
Use 3x3 or 3x5 rear arms the kits are almost the same price and you get more travel. Handling is a function of how well camber, toe, thrust angle and bump steer are set up. Both the torsion and coil over suspension will act bad if the alignment is inncorrect.
Don't bother with a engine kit. Assemble the best engine parts you can afford for what your attempting to do. Next you have to decide if you want to race around or cruise. You don't want to build a transaxle killer. Gearing may also need to be changed. There is quite a price difference. What are your plans for cylinder heads. You also need to include an upgraded oiling system. I just came back from a 70 mile ride with someone who had a Holley carb on a 1915 it kept loading up in rough terrain. He never fouled a plug but the mileage and rings were suffering. A single or dual off road Weber IDA carb(s) might be easier in the long run.
Just run a dyno max muffler. That way it is easier to hear pinging, broken fans and other problems before they become big ones. Make it a slip fit with a side by side bolt through clamp if you want more noise. A muffler might need two of them.
