Not sure how old your 743 is but Bobcat still has the later model covers in stock. It looks like the oldest model had a single cover (6563590) and the later models had two smaller covers (6565196).
This site has the later, smaller cover:
Blower Housing Cover. Part No. 6565196. Used. Bobcat.
www.wengers.com
They all look like they would be pretty easy to fabricate out of sheet metal.