Higher RPM is unlikely to cause the knock, assuming the advance was limited to 22° BTDC - the spark would actually be retarded for that speed. A cause could be valve float (and piston contact), but in a well-built engine like this, unlikely.

Longer-stoke engines come with a lower max RPM, which is a mechanical/physics limitation, not ignition.

A Gear Vendors OD makes sense for an engine designed for lower RPM. I'd try to find a torque curve for that engine, as you don't want to find the GV would lug it with your current diffy ratio. Ideal efficiency would be about 100-200 RPM above max torque at cruise, using rule-of-thumb.

Thanks again Rusty, I just got off the phone with the gentleman who had this motor built.
I was able to pick his brain of what he remembers,

He told me Torque - Man recommend a 650 cfm carb, after he already purchased the 750.

The Maximum RPM is 4500,not the 3200 I came up with.

His thoughts on the engine knocking is octane.

He also told me his goal was to build motor that could pull a house with the best fuel economy.

Everything this motor has with the exception of the Carburetor was what Torque-Man specified.

I going to check but I'm pretty sure the Carburetor I have on now is a 650.

I'm hoping that by the end of the month it will warm up enough to get back to work on it.

All this cold weather is really starting to give me cabin fever.

Glad you got more info. Timing, compression ratio, and octane rating are interrelated...it wouldn't hurt to try premium, because the compression ratio is higher than the rule-of-thumb 9.0:1 for regular.

You might get by with mid-grade.

High test is all I run.