James, welcome!
The 1811 is a wide frame. A narrow frame would be the older
<FONT COLOR="ff0000">I</FONT><FONT COLOR="000000">H</FONT> built Cub Cadets such as the 70/100, the 71, 1x2/3 series, the 72, 1x4/5 series and the 73, 1x6/7 series. When we refer to a "71, 1x2/3 series" that would be these models: 71, 102, 122, 123, the "72, 1x4/5 series" would be the 72, 104, 124, 105, 125 and so on. The wide frame Cubs would be the later
<FONT COLOR="ff0000">I</FONT><FONT COLOR="000000">H</FONT> and MTD built Cubs starting with the 86, 1x8/9, then the 800, 1200, 1250-1650, aka the Quiet Line, and then the 82 series and beyond. Your 1811 is similar to the 82 series Cub Cadets. The model 450, 45" snow blower is what is called out to fit your 1811 however I believe a QA36B or QA42B snowthrower will also fit.