8.75 axle prep help

I finished my front end rebuild last week and have now started looking at my next project. I have an 8.75 housing that was cut and modified for my 73 dart. I have the axles center section, and backing plates.
I know that the spring perches have to be on 43" centers, but how do I get the right angle ? Or would it be better to have this put together by professionals? I have yet to find the "Axles For Dummies" at the local library, but I prefer to do as much myself as possible.

I have time as I do not push the 71 340 for fear of needing a street sweeper to pick up my pieces of the 7 1/4 .