Do you have a picture of your installation? I will try to take some pics this weekend of my relay hookup.
I don't think you want a brass flex plate. If you have a place near, I would suggest just getting one from a salvage yard. The other good thing about that is if you can take it apart yourself you can confirm that you are installing yours correctly.
Another thing about your wiring - Make sure that you have a shop manual. It will have the schematic and you can use that for reference.
Also, you may want to stop installing new parts until you get what you have working. You don't want to just keep adding problems as pretty soon you could end up with multiple things wrong and the more that is wrong the harder it is to isolate the problem because you could fix one problem but because something else is wrong you don't know that you fixed part of the problem.
On these old trucks you have to have a good ground and you have to ring out each wire individually to make sure each one is good.
