The 337 does not weigh twice a Mercury engine. It is heavy. A fellow on the HAMB put one on a scale to get actual weight, 700 lbs as measured:
https://www.jalopyjournal.com/forum/...athead.832985/
I agree it doesn't make sense to install one in a 41 Ford. You have to find a McBar adapter (made in small numbers in the 50s) or make your own version. Anything is possible, but not a compelling reason in this case.
The three people I am aware of who have running 337s report very good performance. The report that most surprised me is the guy who has both an F-6 cab over with a supercharged Mercury engine and a pretty stock 337 in an F-7 four wheel drive conversion. He reports the 337 out performs the blown Merc:
https://www.ford-trucks.com/forums/9...l#post10631326