Hi Mitchum,

I wouldn't be too concerned just yet.  For a mature cat, Oscar has just
undergone a considerable lifestyle change.  Cats like steady routines, and
his has been radically altered.  Perhaps more important, another person is
feeding him; it will take him a long time to get used to these changes.
Keep trying with the tinned and pouched wet food; he liked it once, so
there's no reason why he shouldn't eat it again.  Never just give him fresh
chicken or tuna for humans, as this does not contain all the vitamins and
trace elements that he needs.  A diet of human food only will lead to
blindness.  When you offer fresh chicken, serve 'senior' Iams at the same
time, and this will provide everything he needs.

Do not put his food too close to his litter tray; well, you wouldn't like
it, would you?
Do not put his food near a busy thoroughfare, as cats like to feel calm and
secure while eating.

To help him bond with you, see if he will sit with you and take treats from
your hand.  Once he gets used to taking food from you in this way, he will
begin to trust you with his other food.  Don't give in to him too much,
though; he's got to learn that you can't keep replacing his food.  Leave his
food down for half a day and see how he copes.  Hunger is very persuasive.
Also, some cats prefer their food after it has 'stood' for a while  ..
perhaps to let it warm up, perhaps because they prefer it a little sour.
Perhaps he doesn't like you watching him.

Remember also, that cats develop furballs after grooming.  These are usually
discharged naturally or are vomited.  It may be that Oscar has a persistent
furball which he is finding it hard to discharge, in which case he may seem
to cough or retch.  He needs access to grass, which he will eat, to help him
vomit the furball.
Another possibility is a painful mouth.  Does he seem uncomfortable (rather
than truly fussy) when he eats?  Either of these problems may require a
vet's attention if unresolved, or even if you are still concerned.  You will
need to register with a vet at some point, and change of onwership is not a
bad time.  If possible, it is obviously better for your cat to continue with
his existing vet, who will know Oscar and have his records.

Hope this helps, and good luck with Oscar.
Spider