Nice project you have made so far GregG.
On you sub-engine sizing the trick is too load down that engine so it WILL want to suck volume and negative pressure.
A 208cc electrical generator engine 2000+ watt electrically will volume pull much more than a running, unloaded 500cc engine.
And you will benefit from smaller chunk sizing your input wood.
Using a “fast” wood species/cut-portion too versus a “slow” wood species/cut-portion will make downsizing with small engines tolerable. Dry fast energy releasing sap-wood versus slow energy releasing heart-wood. Conifer wood versus a true hardwood.
Your after blower valving seem to be set up for your intended split blower and engine simultaneous operating?
Strongly advise you skip trying this with a single cylinder engine.
The blower sucks continuously. Will suck much better with as large, and straight outlet pathway as you can give it.
The engine sucks/pulls in short gulps. Doing no gasifier pulling most of the time percentage. "Wait, wait, wait, one short gulp-suck . . . then wait (compression stroke), wait (power stroke), wait (exhaust stroke) again until, the next single intake stroke-gulp.
These two systems will pressure waves conflict. And really, really screws with getting a balanced mix continuously into the engine cylinder!
Ha! And gas reservoir damping work-arounds; and one way flow check valves; have the tendency on engine sudden unloading (someone tuns off the electrical loading/gear shifting) to back pulse backward and one itty bitty tiny hot char pulse sucked engine side, or gasifier side to spark ignite and go BOOM.
On your before carb, or air cleaner box substitute mixer; you will have to NOT port back in the factory crankcase ventilator tube. Just let this tube out to atmosphere with a gauze screen on the end. Crankcase “false air” pulses will drive you nuts.
You wanna’ get going soon with out even more projecting, just buy a bag of “cowboy” “natural hardwood” grilling charcoal and smash size it down inside cloths, screening out the crushed fines.
tree-farmer Steve unruh