As an experienced diver who has done survey work and underwater recover (I used to hold a part 4)
I really really do hope that if you do go down the recreational call to arms you have someone with a clue who is organising and running the whole thing with an iron rod and whip/tazzer.
As much as I can understand your will to do what you perceive to be the right thing what your undertaking is getting pretty high up the risk level for recreation diving. Lets not have another death please.
If this was undertaken as a commercial job all the divers would be on surface demand and there would be a rescue diver suited up. A de-co chamber would be on-site.
The lifting of a 200 plus KG lump of metal which is covered in sharp edges and not designed to be lifted underwater is also not to be taken lightly. Also as well you won't be able to follow the familys wish of leaving your friends body where it rests.
Not to go into details but the AIBB and insurance company's will know exactly what the score is and personally I would suggest you leave well alone if they don't want to recover it.
I must admit this reminds me a lot of the Trident trawler up my way. In the end an oil service company dropped in and recovered the bodies while transiting back to port while blowing the divers back up from 500m. Knowing one of the bosses of said company one of the reasons doing it was A) the divers were good for 70m anyway. B) he didn't want to read in the news papers of someone getting killed trying to recover them on a rebreather.
I will state now if there is a head line of a fat baldy Scottish pilot fatally crashing into the water please please leave me in peace and don't risk anyones life recovering the lumps of meat/bone left. I am more than happy for my remains to be left in Davies locker.