The leather belt that fit the 66 so well was way too tight for the 306. I had to install the coil spring belt . It took me about 5 minutes to do so. I also took off the bobbin winder. The belt rubbed against it and the noise drove me nuts. The belt does rub against the metal lift spring, too, but I buffered that with some tape. I know, I know, TACKY.
Still, the stitch is worth it.