I doubt if the added thickness of a washer under the front plate
would make any difference. These trucks run decades with the
rubber mounts turned to jelly from being oil soaked.
If it were me, I would weld up the plate and re-drill it. But
you're not me and I don't know how far you want to take it. A
1/8" shim drilled to match the mount or two washers between the
front plate and mount would be a quick fix and simply replace
the standard thick washer with a thinner one.
dg
