Bike bandit has exploded diagrams of the parts used in mounting. Not the best in clarity but it is pretty self-explanatory. A month ago I would have been able to get a pic of the area.
Did you find 77/78 exhaust ? Earlier models used a different mounting than 77/78 did. You CAN use earlier systems, but you will need to change to the earlier mounting.
I did some looking and David silver spares has some pipes left, new, unused. Very expensive.
They also have genuine points too. overseas though, so prices will be higher and so will shipping.
There are other options, but it sounds like perfect stock is your goal.
The ride IS the adventure. The destination is just to get gas!