the C code (for '93) and the K code for 94 are factory turbo engines.
the M code is N/A engines.
F would be the power stroke.
ATS built the turbo kits for the turbo engine.it's a wastegated 093.the air filter chamber read "FORD"
you'll see some people with aftermarket ATS 093 kits as well.those read ATS on the air box.
like Gary stated however,these trucks are old.engines have been replaced in many of them.you'll want to insure it's a turbo block before getting carried away.
http://www.oilburners.net/forums/showthread.php?35121-Turbo-Block-Casting-Numbers
if you discover you've got the turbo block,you'll then need to decide if you'd rather have a n/a block.one of the reasons being,the turbo blocks are externally balanced differently and should you need a flywheel/flexplate or balancer in the future,they can be like looking for a needle in a hay stack!
if i ever was going to reman an idi,it would be the n/a 7.3l and id sleeve it.however id personally never do it because i feel the engine isn't worth several grand.id always go used due to them being so plentiful and much cheaper.that's personal preferences though.