I couldn't really get the light just right for pictures of the new pin. It's still in the white and needs to be parkerized. It will be a faithful reproduction of the original Model 601 front pin, only scaled up for the SP1. No, there's no divot on the flat head side, only on the small end.
In addition, the part of the pin that protrudes from the receiver will be rebated to .250 so that it will look more like the original pin protruding from that side. It will have a divot as well but we are planning on making them with and without divots so that SP1 owners can choose the early or late style.
The shaft of the pin will stop at the edge of the receiver. Depending on your SP1 receiver it should sit very close to flush or within .001. I've measured at least 20 different Colt receivers and there is as much as .004 variation in the width where the pins go through so this is by no means going to be a bulls eye every time but the end product should be very aesthetically pleasing even if it is off by .001 or .002.
The head of the pin will be about the same size as the rear takedown pin head, around .373 to .375 so it should look balanced.
The pin will be retained as the original with a spring loaded ball bearing. In case you were wondering, the SP1 has a gap on either side of the front lug on the upper receiver and there is ample room for a ball bearing to engage. There will be more pictures to come and the new pin will be posted on the EE when they are in production.
If someone has some dimensions from a real 601 pin head I'd be interested in knowing the diameter and thickness of the head. The overall length might be of help in determining the length we use for the .250 protrusion.
Thanks guys!