LPG vehicles have a liquid to vapor converter. This converter has hot water from the engine running through it to stop it from freezing. I have it connected to the thermostat housing inlet and outlet that normally go to the carby manifold.

Problem is that it can freeze before the thermostat opens. I have fitted a Davies Craig heater circuit assist pump, however I would like to know which direction the water runs so that I am not flowing against the natural flow with the assist pump.

pretty sure the flow is from the water pump through the convertor then back into the thermostat. you want the water getting warm, if it has to wait for the thermostat it won't get warm.

Freezing isn't from a lack of heat, it's from a lack of flow. Even cold water can stop a convertor freezing, as long as the flow is maintained.

The small hose fitting on the radiator hose outlet of the water pump on a 6 is the "suction" side, and yes, this would go to your convertor's return coolant line (normally it would go to the heater core).

As for "pressure" to feed it, the small fitting at the thermostat housing is constant flow - ie it bypasses the thermostat, so it can be used as the coolant feed for the convertor. This would normally feed the heater core. So basically plumb it as you would a heater core (without the tap), and it will have flow at all times, even when the thermostat is closed.

This is how I have my VL plumbed (albeit off a Holden V8 - but the bypass hose from the 2nd thermostat outlet feeds back to the water pump as per factory) and it never freezes, as it always has a consistent feed.

There's 2 ways to hook the heater up - either in series (after the convertor) - but this only works if it's a full-flow core, or in parallel - which is the only way you can do it if the heater has a water tap of some variety.

Parallel is probably the best bet without knowing the intimate details of your heater setup.

To do parallel with only 2 heather hose fittings (one suction, one supply) you just need to nut it down to a "supply" line, and a "suction" line. You can run a T-piece off the supply, to feed both the convertor and the heater.

Like the supply side, a T on the suction line (from the barb on the water pump), drawing from both the core and the convertor, will service them both well.

Now you're probably concerned about flow, but both the converter and the heater core are restrictive & don't require the full flow that a 5/8" heater hose can deliver, so you won't usually starve one or the other, but in really cold weather it's best to leave the heater tap off to give as much flow as possible to the convertor until there's a bit of warmth in the coolant.

If you do have issues (rare, but it can happen if the water pump isn't performing) you can put a small restriction in the heater supply pipe, or limit the travel of the heater tap.

In that case you have to run it in parallel, as described above.