That is backwards. The colrifier must be in the engine return water path,
not the engine feed.

Not so. Calorifier connections can be taken off and returned before
the thermostat housing or either side of the thermostat housing - out
to cal before thermostat and return after, or worst case both after
the thermstat housing. I had a calorifier coil connected the second
way and engine had no problems heating up to correct temp. In fact I
now have a substantial heat exchanger in place of the calorifier so
that the engine heats up the entire CH system - 2 calorifiers and 14
radiators. When I had an airlock in the keel cooling system, engine
cooling was achieved using the radiators.
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