Drop and cast are much more important than LOP when it comes to gun fit. LOP may affect how well you can mount the gun, but when it comes to shooting where you are looking, too much drop or too much cast are a bigger issue than a stock that is too short.

Cast and drop can be fixed by bending potentially - my success on that front has varied, as it seems to depend on the wood involved and the amount of change needed. If the gun in question is close to your dimensions, then bending may be an option.

If your are going to order one, I would second the suggestion to have it made on a 20 ga. frame.

Such a long, long time to be gone, and a short time to be there.