Hi I have a W&G lock stitch too and use it as my main machine. I have an 11-A, a bit newer than yours; it has the auto-lubricating unit on the front but otherwise it's identical. For needles yes you'll need a round shaft needle with the groove and the needle is inserted with the groove to the right. Organ still makes them, the size 16 needles I have are marked LA X 1617 75W SY8780. Also, to change the stitch length hold down the silver button on the right side of the head (to the left of the wheel) and then turn the wheel (either direction is fine) until it engages inside the machine (you'll feel it.) Then keep turning the wheel until the stitch length changes. This is an industrial machine, very fast, it runs about 4,000 spm at full speed. You should be able to fit it into any industrial stand and it takes a clutch motor. The only negative thing about it is that they have not been manufactured for decades and parts are impossible to find, when the timing belt goes it might be history. But enjoy it while you can! I did some blog posts about mine and here are some photos:
http://coudremode.com/mccalls-5525-s...different-sort
Also there is a link to a Smithsonian site where you can download a manual. I also have a threading diagram if you need one.