The French flathead IIRC doesn't have a thermostat. However, the origin of the engine design (those lovely exhaust pipes through the block) were a Henry Ford stipulation - it would enable engines in the extreme cold of a Detroit winter to warm up rapidly (and with them the occupants).
The original engines were renowned for overheating in warm conditions - the original pumps were pitiful things and the blocks suffered a lot from poor casting - this was the first V8 block cast in large quantities and even the skills of Cast Iron Charlie (Sorenson) weren't up to coping with Henry Ford's refusal to countenance proper cooling. After some 700,000 unhappy customers the engine was substantially re-designed and cooling significantly up-rated. As one Allard owner put it to me, he has met soldiers from the desert campaign whose Bren carriers were flathead powered all the way through the desert without once overheating.
I suspect the block crack is more the cause than the result - even tiny fissures will pump exhaust gas into the cooling (hence the block tester colour) and of course, this will shove up the operating temperature. The 21 stud in the Allard is an early engine so the waterways were heavily furred (and silted - the original casting sand) up - we suspect it had never been cleaned out. My car had had its engine fan removed and replaced by the previous owner with a Kenlowe, which was thermostatically controlled. Helpfully on the day I picked it up, the manual over-ride fell off, it turned out the battery was not being charged by the alternator, and the car over-heated going up the hill from the A23 clockwise round the M25. The orginal Allards also had a cowling from the front grille to the radiator pushing all the air into the radiator - mine had had it removed at some point - so yet another source of poor air-flow.
The garage doing the work looked at the set up - Kenlowe, rotten radiator, overflow tank and reckoned that overheating had been a common problem for a long time, so reckon the crack was long standing also - three recent engines they looked at were very similar, but the labour in stripping them down would cost more than a new engine. Hence the French flathead. This has significantly better casting and metallurgy (plus much larger water channels that the stronger cast allowed).
To put things in perspective, the garage owner runs a Model B hot rod which doesn't even have an engine fan, but has a good radiator and water flow (plus much better exhaut than standard) and he says it doesn't get close to over-heating even in heavy traffic.
