The leather belt will probably help you a lot. When you first get it, take an end in each hand and stretch it across your shoulders. If you stretch it enough, you probably won't have to adjust the belt for a good long while afterward.
Then, practice. A lot. Sew without thread or chain-piece blocks or whatever you want to do. After a couple of days, you'll be able to sew one stitch at a time using only the treadle.
The 66-1 has no reverse, so to strengthen the ends of seams, either turn them 180° and sew back for half an inch or (as my grandmother taught me) just pull on the fabric to slow the feed for the last half inch - this puts the stitches very close together.
Honest, you'll get the hang of treadling very soon with a little practice. I love using the treadle when I need to pay attention to where every stitch will go.
Or when the power goes out. Last time we lost power for a few hours, the other humanoids in the house were whiny and bored but I couldn't hear them - I sat and sewed with my iPod in, listening to old radio shows from the 30's & 40's.
Have fun with it and don't be discouraged - you feel like you have a couple of extra feet at first, but that goes away pretty fast.
