Good hearing from you in Martinique!
First of all I think you would agree not to use an aluminum version in a marine application. As for the iron versions, they would work as well in the LH as the RH application, because the block doesn't really know the differnce. Piston thrust in one direction would essentially be the same as the other direction, only on an opposite side of the cylinder bore, exactly like the standard Ford 427 block didn't know if it was going to be used in a LH or RH mode.
What may be a challenge, would be the flycut bosses necessary for the marine motor mounts, or some issue like that. In talking with many of my automotive 427 friends about marine motors over the years, I think that is essentially the only difference between the marine and automotive blocks. If you had an original block, you could take it to a machine shop with the new block and say, "make me one just like this". As far as I know, all the other ancillary devices will bolt to this new block, and I think you could have the bore specified to just about any bore you wanted within the limits of the casting.
Since this casting has more iron, it can be bored out to larger piston size. These days if you need new pistons in a 427 you're talking about a custom piston, but so many people are doing it in the Cobra replica business it's not uncommon. My spare 427 motors for instance, have Keith Black custom pistons.
I think virtually ALL of the marine manifolds, heads, intakes, transmissions, etc., would bolt up to this new block as well as the original block, with the exception that the new blocks are not specifically intended for industrial/marine use, and have not been milled for the motor mounts.
If you had a block failure, for instance, you could use your damaged block as a guide for any additional milling necessary to make things fit up. There may be a threaded tap somewhere that would need to be done too, but the blocks are supposed to be a swap out with the original. The tech guys at Genisis would undoubtedly be a great resource if it ever comes to this.
As I recall, your 427s are side-oilers, and the block Genisis is making now is supposed to be identical. This is important, because the side oiler cam and cam bearings is different than the top oiler can and bearings. Although one will fit the other engine, you must use the right parts if the oiling system is going to work properly. If you are ever seriously considering one of these blocks, then you would need to specify the exact bore you wanted, etc., and the cylinders may need to be honed once they arrive, etc. I don't have any personal experience with Genisis, but I've heard good things about them.
You could build a monster, or you could build another 427 using the exact same crankshaft, standard bearings, etc. Since marine motors spin slower, it would be fun to build a torquemonster, but the stock 427 sort of already fits that billing with 438 footpounds of torque at 2900 RPM. Torque has never been a problem with the 427.
The standard cast iron crankshaft is a superb piece of equipment too, and really doesn't need to be replaced (unless this is one of those "because I want to" projects).
I found out a long time ago, that "because I want to" is a valid reason for people to do things. Many years ago I told my Grandmother that "because I want to" was a good reason for her to do anything she wanted. Warren Pateman spent around a half million dollars rebuilding BAMBI, his 38' Express (now sold) simply "because he wanted to" do it his way. What he did could never be financially justified. Warren is now gone, sailing smoother seas probably in a Commander in heaven, but his time on earth was enrichened due to his boating endeavors. I thought I'd mention this simply because so many of our decisions are based on financial parameters. If financial parameters are not the driving issue with you, as they were not with Warren, then new blocks at some point in time may make more sense.
For now, I'd run the ones you have and see how they perform.
Hope all is well with you and yours, hope the boat is doing well too.
Regards, all the best,