Ah yes,ye olde go-kart engine.If I recall correctly they made a 580 and an 820 .During the glory days of 2 cycle kart racing these engines were about the only ones that kept McCulloch from totally dominating the field.
The engine or combination of engines were limited to 16.5 cu inches.Two of those 820 s would be 16.4 or .1 below the max.They had a bunch of low end punch,but the Macs had the rpm .Back in the day I remember some real odd carb set ups on the Westbends.3 carbs,I bet that was a real fun thing to tune.
If you do a google search you could possibly find out more info.I also think parts are still available.