I think of the flathead powered M37 wrecker that Jonathan Winters drove in It's a Mad Mad Mad Mad World. I'd like to have an M37 if I lived in a rural town. A slant six can do the job at 45 mph, but as a business - no.

Modern 6 speed trans., 4:88 to 1 gear, keep the 1 bbl and build the engine for pulling, MAKE SURE YOU ADEQUATELY WARM THE CARBURETOR and you’ll sing down the road. I’m contemplating putting one in my t1n sprinter with an automatic, its a cab/chassis with 4:18 gearing, duelly.

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Advise should be taken as ongoing, that way, when you get to realizing what you are doing you can include yourself.