My best advice is to get the imbert spec sheet and build it. For small engine running on very dry wood chips 1x1x3/8" thick use the 2" restriction and drive your geometry to the rest of the specifications.
The Imbert gasifier is not broke, it works just fine. Can it be improved absolutely, but these improvements really have nothing to do with the Imbert reactor. Sort of like a car engine that is designed to run on gasoline. Put grease in the fuel tank and it wont run. Put water in the fuel tank it will run poorly if at all.
Again it boils back to the Physics, and generally this requires automation to over come them. At least for the smaller scale, small engines. The WK gasifier is much larger and fuel flows are much less an issue. But these small engines, you are pretty much going to need to use automation. If you find your self putting efforts into filtration you are taking a wrong approach, nothing can be done with tar after it is produced post reduction. It is carried in the gas as a gas and will stay in suspension until it reaches atmospheric pressure near ambient temperature. The only way to filter tar is via a micron level filter that would need to be regenerative. This is simply just not going to be practical for running engine and besides you can create tar free gas if you get the physics of the process under control and tuned parameters within the means of what the gasifier is capable of processing.
Sniff too much of this gas and you type like me!!