I would be happy with 60 on the flat and 45 on hills towing 4 tons or less for distances less than 2000 miles.
I probably wouldn't haul anything heavier than an engine-transmission combo on the flatbed although it may have a standard load of a couple hundred pounds of tools.
I don't have a firm idea on engines yet. I love Diesels, but don't like to work on them, so that path is out. The only four engines I'm seriously considering are 250 I6, 292 I6, 262 V-6 or an SBC. I guess the final decision will be based on a combination of cost and availability, both of the engine and parts for it.
