I have knee action shocks on three of my 49's. The only one I have here at the house is a 3600. It has the yoke with threaded rod, which is the double acting shock, my 3100, and 3800 both have single acting shocks, which have yokes at top and bottom.

My 3600 lower plates are flat. with the hole at the front of the spring U bolts. So that the yoke/threaded rod goes straight into the plate with rubber bushings on both sides with a cupped washer on the outside of each of those, then the nut.

I could not tell you about the others because they are kept elsewhere-

Sounds like you have double acting shocks- the have a big threaded cap at front and back- the shock arm mounts in the middle. Maybe someone replaced the lower mounts with tube shock plates for some reason?

does your shock look like this?
double acting



or more importantly, do the lower mounts look like these?
lower tube shock mount



1949 Chevy 4400 Big Red
1949 Chevy 3600 Bob's Truck
1949 Chevy 3100 The Investment
1949 Chevy 3800 the Won Ton