C'mon guys. Am I the only engineer on here???
I weighed my old Jeep back in high school with a bathroom scale! Been so long I forget the exact setup, but it was simple.
As I vaguely remember, I used an 11 foot 4X4. Put the tire 1 foot from the end, scales 10 feet away, small block under the short end.
Zeroed the scales with just the wood first, then eased the tire up on the beam. Multiply the reading by 10.
150lbs equals 1500lbs.
Mark the beam so each tire is in exactly the same place, make some small ramps so it rolls up smoothly, and you're in business.
An aluminum I beam would do better, less flex. You have to be sure the beam does not touch the ground.
And, you might have to adjust the length of the beam for different weight trucks.
Most scales will go up to 250lbs, which would equal 2500lbs per wheel, or 10,000lbs per truck, so most of your K5s would work fine.
Might not be accurate down to the pound, but should be close enough. Plus if you were wanting to check how each wheel relates to the others, that should be fine, since all of them would be the same amount off.
Just a thought.........