Vincent.vanGinneke wrote:Eat this
Nice one

.
Another thought . . .
I recently replaced the front springs on my
Ifor Williams HB510 Horse Trailer. Its a twin-axle with a gross weight of 2584 Kilos.
The front nearside cops all the sunken drain covers, broken kerbs, rocks at the side of the road and so-on when towing around the narrow roads we have here. The front N/S spring broke

.
The springs are single leaf parabolics, they cost £36.20 each (including 20% VAT).
Ifor Williams make lots of trailers in different styles and capacities - there must be a parabolic spring that would suit your sidecar.
You seem to be going to a great deal of effort to modify something that may not give the result you want.
But keep the pictures coming I'm looking forward to seeing the build progress

.
Bob.
My avatar shows the late Len Rich in 1970 with the bike I now have - a 1958 Ariel VH