I built mine in a handful of weekends. It wasn't that long for construction. It is a four post design with acme threaded rod (5 threads per inch) to raise and lower the head. I used a 5 horsepower industrial electric motor that I pirated off a grain elevator. It is a "man". I had another newer model 5 HP on hand and it doesn't have near the power of that 50 year old unit. The rails are 4" angle. Cross bunks are 2x3 box tubing. Blade guides are generic stacked bearings from Agri-Supply. The acme rods are hanging in pancake bearings at the top. Compact spare tires were pirated out of Lincoln Continentals from the pick a part yard. Axles are Ford 9 inch, but I had to turn them to fit the pillow block bearings I used. I have 24 feet of rail and can saw about 22 feet. There is about 27 inches between blade guides when fully open.
I had a metal cutting bandsaw and an arc welder. Take your time with your welds so you don't warp anything. I had some movement on my four-post and had to do a little manipulation to get it squared.
The two acme rods are connected by #40 chain. Notice the 3/4 bolt on top of the right hand rod. I can sit a cordless drill on it and power the head up and down. It will move quickly. The steering wheel on the other side is for minor adjustments. The acme rod will hold its position. It does not move during operation.
It will saw. That's my log arch sitting beside the green house behind the mill.
It is a 3/4 ton extended cab Chevrolet pick-up frame. That's a 12,000 pound mile marker winch on top. I built it to handle tree length logs for a log cabin.
Wudman
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. sorry could not find a cup of coffee. We will have you thinking like an old man soon enough. 
Might even want a remote on/off switch to start and stop, esp. if the stuff hit the fan.
