What confuses me is why you want a Monte Carlo and an adjustable comb. Why not just have adjustable combs installed in both guns and raise the comb as required?
Monte Carlo stocks raise the head in relation to the bore resulting in a gun that shoots high. A high shooting gun is good for trap because the birds are rising while not as good for skeet, sporting, etc. where birds are crossing, rising, falling and all points in between. Sporting guns are generally set up to shoot flat.
Any reasonable gunsmith should be able to install an adjustable comb and then you can adjust it to suit your needs.