EK, patience, patience. All will be answered with time. First, you need to get your kit in your hands. Then all this will start to make sense. The trunion screws have nothing to do with the head-space. There are three rivet, or if you prefer, screw holes on each side of the trunion. They secure the trunion to the receiver. They do not secure the barrel in the trunion. That is done with a steel pin that is pressed in. In mounting the trunion in the receiver, which do you think is best for strength, soft aluminum rivets, soft mild steel rivets, or grade 8 hardened button head cap screws? I think that needs no explanation. It really isn't hard to do. You have the experience to do this. Look around here and elsewhere and you will find what you need. You will need sksman's rails. One each side. Get these ordered, get your kit ordered ( you should get the global kit, it's in stock and I/O's kit is not, also they will substitute buttstocks and I/O probably will not, globals is probably new, I/O's is not, and you get what you pay for. Saving $40 will not matter in the long run if you get lesser quality parts.) But you can do as you wish.