I heard or read there was a "Hyperpack" slant six four barrel aluminum intake & so on, high perf, 225 engine I think somewhere around 1965 year?
I have not heard of any real problems w/the mopar 225 slant six, but then again, I'm a Chevy 250 6 man myself :-)
The 225 slant six is not really a good torque engine for the type of hauling you are thinking about. But you can get good miledge.

12 port SDS EFI