Do you have multi leaf springs or single leaf springs? I was under the impression single leaf spring perches did not have a center hole. Multi leaf spring perches have a hole in them, the head of the spring center bolt goes in this hole, that lines the springs/axles up side to side.
Are the rubber bumpers on the front of the bars touching the bottom of the springs thus forcing the front of the bar down? If so they can be cut using a hacksaw. The spring perches welded to the axle housing tubes are not necessarily horizontal after attached to the springs. If they are angled down use the wedges as mentioned above.
I'll attach a photo of a single leaf perch, a multi leaf perch and photo of a multi leaf with a spring in the perch. Obviously the spring in the multi leaf perch will have to have spacers installed so the spring will be clamped correctly but it gives you the idea. The head of the center bolt on the bottom of the spring fits in the hole in the perch. If you have a perch without a hole and do have a protruding center bolt head you could drill a hole in the perches to accept the bolt heads. The rear axle assy on my 68 is [sadly] from a 69 Camaro, the spring perches did not have holes in them but small indents that the low profile bolt head could sit in.
