Hey,
Congrats on your new machine! The 737 was made in the early 90's. It, along with it's sister machine, the 605, were the first BCSs to have instant reverse. The red lever between the two brake levers engaged reverse when squeezed. The T-bar on top of that handle engages the differential lock. if you release the lock, you can use the brakes to Turn-on-a-dime. Early machines (10000-14275) still had the 18mm spline drive PTO. Later machines had a larger 25mm shaft. This was done because all the attachments were getting larger and BCS was getting some warranty claims of twisted PTO shafts. Joel at Earth tools told me the 30 inch rough cut mower was the biggest culprit. The larger spline PTO was was dropped for a 3 dog PTO with the new series in 1995. I don't know if there is an adpater for 25mm to 18 mm or 25 mm to 3 dog. If your machine is 25 mm, you'll need to talk to Joel to find out your options if you want to put any other attachments on it. His site is Earthtoolsbcs.com
Your engine is probably an Acme 10 horse gas or 8 horse Diesel. If it's not running or not easily fixed, you may be money ahead to buy an adapter and newer engine. Joel is the only person I know that still supports Acme engines. They exited the US market in the early 90s. They were supposedly very good engines, but I have no experience with them.
They're great machines. Let us know if you need more info.
Bill in WI