re S30's reliant on the steel roof, some older cars are?
The S30 is a "unitary body" or "monocoque" type car.
The inherent integrity and strength of such a shell is acieved by welding together all the individual smaller pieces. Every piece whether it is a small box section floor member or a curved side or top panel that is weldedin contributes to that overall strength.
Removal of any piece will have a negative effect on the overall strength of the shell.
Im not an engineer of any description lets alone a structural one but IMO removal of one of the largests panels and destruction of 50 odd welds plus some brazing/or lead bonding is going to have a huge negative effect..
Will a fibreglass panel stuck on with some tubes of Sikaflex reinstate that strength and integrity???
I dont have the answer but maybe you should have looked in to that before hand?
If you are building a race/track/rally/drag car with a full T45 multipoint fully welded in cage then I see no problem.
S30 doors are a little self contained "monocoque panel. The strength and integrity are dependent on a number of smaller steel panels welded together according to a skilled design.
Removal of one large panel from a door will weaken it. Once again im doubtful that replacing it with a fibreglass panel which will only be bonded on a very narrow(10mm) edge will replace that strength.
Have you considered the SIP implications?? Do your doors have substantial SIP bars already? Or are you planning on adding them.
I hope nobody on this forum is ever involved in a serious motoring collision/accident with their car but what would an accident investigator or insurance loss specialist make of a car with these mods?
And would you or any other owner contemplating doing the works advise the insurance company of the modifications.
I know i have droned on a bit but TBH Im personally worried by what you are proposing.
Value and aesthetics are also issies that deserve some thought.