I wouldnt add an adjustable sheek peice, aluminum is gonna be cold on the check. Instead, i think that two vertical "runners" on either side of the stock so that your stock could accept an fiberglass/composite check rest.
Looks like you have put some time into this. Is that a picture of an autocad entry ready to cut?
When I made mine I just made the whole thing from well behind the bolt to the forend tip one solid piece . That square forend tube looks ordinary and the joint is a place to get flex . A round forend tube would look way better but getting it low enough is a problem .
I would be inclined to make it more like this stock. ( not mine below)