I can't weld aluminum to so??? I tried those so-called aluminum rod kits that require mapp and they do work but over time the weld turns dark gray. I can mig weld and braze weld. If I need a aluminum part I machine it. That look like what you need. Im not totally convinced on composite? You might try Ebay for all Aluminum kits. The flex shaft you can use the one from a trimmer. All you need is the square end and cut it to length. Silver solder (Stay Brite) the brass furrel on the end and away you go. The shaft log you can get at Menards as I stated before and you can find the teflon tube liner online. Most important thing get a resistor spark plug or you'll have noting but headaches trying to fix the problem.
A Homelite 25 cc engine is going to be far better than that craftsman. I recommend the st135 Bandit. No clutch but you really don't need one. It's nice but the clutch shoes are really crappy.