401 Cooling

[MKTR401]

Good day everyone I am new to the thread. Have owned a 401 for a number of years and have been enjoying incremental improvement. My 401 has an early water pump (no thermostat), but is missing the shutter assembly on the radiator. So effectively it’s running without a thermostat. As the seasons change in uk, I have used different sizes of card to blank portions of the radiator. It works quite so the running temp sits in the range 75-85degC, but is not elegant. I have seen that a Renault 5 thermostat exists that could fit in the top hose, a relatively easy mod, and less that £10. So my question would be when that thermostat is shut effectively blocking the top hose is there a bypass water gallery where the pump mounts on the block that would effectively allow the water to circulate around the block e.g a bypass without going thro’ the radiator.
Any thoughts?