Whenever I’ve had the abutment plate off the way I reassemble it is to place everything in position loosely and then twist the throttle capstan fully open and basically let the thing centre itself, with the butterflys fully open, and then tighten things up. If the throttle rods were the correct length to start with then I believe that is as good as you’re going to get it with no need to adjust the rods.
On later engines the ribs weren’t exposed.
The whole cam covers were black. Yet another penny pinching,cost cutting exercise by the “Leyland Cars Ltd”bean counters!