...My objective was to ride a longer board from the tail. ...
Yes I think you are on the right track there. Narrow nose, wide point back, wide in the aft region will all produce a board that allow you to stand further back and turn some extra length of board more easily. You don't have to incorporate all 3 of these - when I saw the title I pictured the original pig longboard - quite wide, sort of cigar shaped thing and I thought of the McCoy Nugget. This has a narrow nose, very wide in the aft region, it looks like it has wide point back, but that is an optical illusion, when I put the tape measure and rocker stick on one I borrowed it is exactly in the middle. The one I borrowed was 6' 6" which is an enormous amount of litres and planing area for me. Despite this it did top to bottom turns really well once I got used to it and had really good sort of drivey glide. Keeping the wide point in the middle stopped it from become too pivoty and lacking drive.
In comparison I borrowed much longer ago a copy of a Schroff Blaster (mentioned by
@enframed above) - when I say copy, the owner had put in a custom order for a copy based only on a photograph in Surfer magazine, so it probably was completely different in all but outline. This was a short board and it went awful for me - really pivoty, no drive.
I also borrowed a copy based on an outline pic alone of one of Cheyne Horan's most extreme Lazer Zap outlines - the one with a "bum" tail - that's what we called them anyway due to the way it resembled buttocks. Because it had so much planing area it did motor along quite well in a gliding way - unlike the Blaster copy which didn't really want to go anywhere for me. This Zap design was not drivey though.
I didn't measure them, but I think the Blaster and Zap copies I borrowed would have incorporated all 3 of those pivot aiding qualities I mentioned.
Because you are going for 6' 10" in length that's going to help stopping it from becoming too pivoty. Also judging by the pics you posted of the retro short boars it looks like you aren't after anything with extreme width in the tail, so I reckon you could combine all 3 of those qualities mentioned i.e narrow nose, wide point with some area towards the fins by adding a bump wing or some extra curve in that region - as mentioned by
@Swallow Tail
@casa_mugrienta posted a nice video of Creed McTaggert ordering such a boar. I really enjoy watching Creed - his regular ride seems to be longish HPSBs and he makes them look good. It seems Creed didn't score great waves, but demonstrates that it can be ridden in regular waves. The shaper Ben Webb features in the vid and puts on a good display of this design. You could go to his website and look at his "Vault" design for inspiration.
Would like to hear your thoughts @griffinsurfboard
forum.surfer.com
I look forward to seeing what you produce, I'm quite jealous that you are in a position to whip the planer out and quickly iterate thru designs! I am not sure if I am going to have enough time to do my annual build this year. If I do it will be iteration 4 of my computer design over 5 years - a painfully slow way to develop a design