One thing to be cautious of. I can't remember off the top of my head if a 200 spindle is a 1-1/8" X8 tpi or not, which is both the same as a 10" Logan 800 series lathe and the South Bend 9".
A chuck is supposed to go all the way over the non-threaded part of the spindle and "seat" or "register" on the lip of the spindle next to the head stock. Not stop going on the spindle when the threads end. The 10" Logan Lathes, 800 series, have a longer spindle than some other lathes that have the same 1-1/8" X 8 tpi. So some back plates machined for a different lathe will stop shallow. Logan mentions this on their web site but I didn't think about it until after I had a problem and was learning about how back plates are fitted to a chuck. This means if the space between the back of the backing plate and threads is too shallow, the back of the chuck doesn't register on the spindle flat. The chuck will register at the end of the threads and not be square to the spindle.
Learned this when I was trying to figure out why I was having so much trouble with the 3 jaw that came with my lathe, Wrong back plate. Only way to "fix" the back plate is to sacrifice some threads so it will seat on the spindle register/flat. Too many irons in the fire, set aside for some other day.
I did a quick check, my Logan 4 jaw has ~ .349" between the back plate registration and the threads.
What I "assume" to be a back plate for a SB or similar only has .201" between the back plate registration and the threads.
Others may want to pull some measurements and chime in so you will be able to check with eBay sellers.
All that said, Take a look at Shars. You may find the price more reasonable than you thought when weighed against what has to be checked.
Ron