Changed my mind about filling the heads of the slotted bolts to create a rivet appearance from the front of the shield.
Decided on using round head bolts, grinding down the characteres on the head and removing most of the square section under the head. I did leave a couple of roughened areas, to catch on the shield metal and prevent the bolt from turning when tightening. I tested this theory, and it does work. Only because the shield is aluminium, so there's another reason for using the lighter metal! Obviously ALL these fake rivets will have nuts on the inside of the shield, but I can live with that. I had been graciously offered real rivets to use, but I'm not talented enough to use this method of fastening. Nor do I have the tools to do so.
So far, I have prepared a total of 40 bolts. 20 small and 20 larger size. Having just counted, I need further 55 of the smaller size, and another 15 of the larger. It took me 2hrs of careful grinding and filing to get the first batch to the condition I wanted. In addition to all those, two brackets will need to be hex head bolts, due to lack of access to rear. I.E: 4x bolts to zero scale block, and 4x bolts to Illuminating Apparatus case mounting bracket (nuts are welded to rear of the bracket itself).