In theory this should be fairly straight forward?

Upgrade the ECU and allow for the different Cats setup. Something that is not needed if you have the upgraded manifolds.

I wouldnt of thought that when Aston released the 4.7 engine ( which for all intents and purposes is a slightly bored out 4.3 by design ), that they would want to change the fitment considerably since that would require costly factory re-tooling etc.

 

I believe the changes to increase displacement were entirely internal, so the dimensions of the engine itself should be the same.

Out of curiosity, I did some digging. The front structure of the V8V and V12V have the same part number. I thought the V12V had to have its front structure widened to accommodate the larger engine, but the parts diagrams I pulled up say they're the same!

V8V
9G33-CSA01-AA Sub assy Coupe, 6.5MY 0nwards-Chassis plate required - contact parts operations
V12V
9G33-CSA01-AA Front crash structure sub assyChassis plate required - contact parts operations
Yes, the descriptions are different, but the parts in the diagrams are the same (with some differences in detail). I'm not qualified based on the little info I have to determine if they're a direct swap or not.

It looks they might have the same front subframe as well. (Sorry I can't give a more precise answer on this, the site isn't working right.)

If that's the case, then you'd just need to check the engine mounts themselves. If the above structures and subframes are the same for the V8V and V12V, then the 4.3L and 4.3L V8Vs should have the same parts, too.

Any of the ancillary hoses and whatnot can easily be fabricated so those don't really matter if they don't match.

 

On Piston Heads it was posted that a 4.7 was available on eBay. Too much trouble IMO.