Propane regulator, principles of operation?

[rkcarguy]

I've been working a dual fuel setup on an EFI motor and am down to the last few things on my Honda.
I have a VFF30 vacuum shutoff/filter, and a Model J regulator/governor.
I don't have the option of running a propane mixer because I want to maintain all the EFI setup.
The model J has a single 1/2" pipe outlet which feeds the propane, AND is also the "signal" from the engine(i.e. it flows more gas the more the engine sucks from it.)
Originally I had drilled and tapped four holes in my intake wanting to have even distribution to each cylinder due to the log style mainfold on the honda.
Problem is, that it's AFTER the throttle body which is going to mess up the "signal" to the regulator. I think it will be backwards, rich at idle(if it runs) and fuel will drop as vacuum drops in the manifold as the TB opens.
The forklift we have in the shop using the same setup, has the venturi ABOVE the throttle body in it's CA100 mixer.
Am I correct that I'm going to have to install a venturi in front of my throttle body in order for this to work correctly?