“….The bottom of the seat is welded aluminium alloy”.

This is a good start.

So in the absence of an original drawing, I think the best way to re-create one of these seats would be to make an aluminium seat pan (lower part) based on a Spitfire one, and use the AP extracts/photo’s you have of the Whirlwind assembly to reconstruct the support fraimng, armour plate, and fabric padding. Westlands made Spitfires, so maybe there was some cross-pollination of design here??

In post#2 you have shown the isometric diagram of the seat. Item numbers 3+6 are more than likely the standard AS seat riser/locking quadrant parts common to many types. You see these on the Hornet/Vampire/Firefly seats I referred you to earlier.

Hope this helps.