Geoleo
Suggest you stick with anon turbo Perkins like you have. As suggested TAD would be a good place to check.
For whatever it is worth, my memory is that the T6.354(M) has essentially the same cooler configuration, etc, as the 6.354(M). This contrasts with the 6.354MGT, which has the "Breadbox" cooler, etc.
I think the max RPM as set in the injector pump tune might be different, 2400rpm (turbo) vs 2800rpm (naturally aspirated). And, the cruise RPM might be different (approximately 2000rpm vs approximately 2300rpm).
So, I guess one would want to get the prop pitch adjusted by 200rpm, or have the pump and injectors retuned to match the naturally aspirated engine (meaning no boost from the turbo, so you could take it out).
But, as long as there is room for the turbo, I think it should fit on the same mounts, have the same angles, get and return fuel the same way, get raw water the same way, etc. Exhaust configuration will be different, obviously. And the blowby tube will likely go to the turbo inlet vs air filter housing, etc.
Obviously one would want to check all of that eyes-on.
Last time I checked with TAD, which admittedly was years ago, they didn't have any cores, so one needed to send them their old core, or buy a core on eBay, etc, to send to them.
The used motors my boat's PO has reportedly have the transmissions with them. But, I don't think he tested those as I understanding his testing of the engines was out-of-water.
Again, if you DM me, I can put you in contact. You shouldn't believe anything I might say about them -- I've never seen them!