Blowing smoke doesn't really mean the rings are shot. First off, does it use oil - yes, then probably rings but could be valve guides and seals. If - no then it probably is a fueling problem (pump or injectors). Compression test can tell you a lot.
Saying it starts with the first turn of the key usually means that compression is good (compression rings good but maybe not oil rings) but valve guides and seals can be bad. It usually also means that pump and injectors are good.
Has someone opened up the fuel pump to try and get more Hp out of it. Is it turboed or was it turboed and turbo has been removed and fuel not turned back.
Myself, yes I think a 4D34 will bolt in with very little modification. But why a 4D33 is a lot better engine but you do need to turbo it.
There are a lot of "maybes" in it I know.
Dan.