Right so havent stopped working on this.
Got the bolt guide set up now, with the spring mod and adjustable length mod. I also drilled and tapped holes wither side of the allen key hole on the back cap, which I'll be loctiting some small bolts into to make it tooless removal.
Basically I drilled and tapped M5 holes in both sides of the bolt guide, I then loped the head of an M5 bolt loctited (248) each end of it and set the length I wanted. I then let the loctite dry with the bolt kit assembled inside the marker.
The reason I let it dry in the marker was because I didn't drill one of the holes perfectly straight so the alignment on the guide was off by a couple of mm.
By putting the bolt kit together it forced the pieces to wobble on the threads pushing it into the correct alignment, then the loctite dried holding it into this position, thats the hope anyway, seems to have worked.
I think Balf will approve of this pic...