Steven’s remarks about the airfilter and access to the timing belt are excellent, and well timed!
The only gasmixer component that need to be reasonably near the current throttlebody, is the double-throat twinflap, former carburettor.
Its syncronized flaps (may be on the same shaft or in tandem).
In tandem = individual parallel shafts with cranks, connected with a connecting rod.
Like the pulling wheels on a locomotive.
Equal closing and open angles. Equal throat diameters.
Connecting route to the current throttle body needs to hold up for vacuum! Needs reinforcement if the double-throat mixer is connected in series with the common throttlebody.
The mechanical operation of the two components in series needs attention.
If room allows near the intake manifold, a parallel feed is to be preferred.
Is there room to make the woodgas-mix intake in the other end of the intake-manifold?
That would make it much easier. On the left side. (car’s left side)