You really have a few options, none of them are terribly good..
1) live with the deeper keel.
2) buy a new shoal draft keel from the manufacturer
3) have Mars (or someone else) make you a new shoal keel
4) cut your existing keel down and bolt on a torpedo
5) find someone with your boat who wants to swap.
Frankly 5 is very unlikely, but would be great if you can, 1 has practical issues only you can answer, 2&3 are variations on a theme and are going to be pretty expensive.
So 4 is probably your best practical option. Mars has in house designers that can design a decent bulb to keep the boats RM the same. Basically you will just bolt two teardrop slabs of lead to either side of the keel and then fair them in. The problem is that as you raise ballast you also reduce the lever arm, requiring more ballast to keep the same RM, it won't be all that much, say a few hundred pounds more in lead than the cast iron you remove but it isn't nothing.
What concerns me, is I think you have a very similar keel to my Beneteau
, which means the bottom of it is much thicker than the top, basically a primitive bulb. So you may have a lot more iron at the bottom than the top. If this is true, you could be looking at a massive bulb to compensate. Instead of the 1,500lbs in the first case it could be double that or more depending on the configuration.
From an engineering standpoint it doesn't make it that much more difficult, but cost adds up. 3,000lbs of antimony lead isn't cheap
. If you needed this much a whole new keel may not be that much more expensive, and frankly would allow a better profile.
Realistically anything you do (other than learning
to live with it) is >$10,000 so I hope it's a very good deal.