Belts, etc. Probably the main reason Fiat arranged the compressor, alternator & water pump that way was due to the drive forces needed to turn the compressor pulley. With the compressor driven straight off the crank pulley, it saves wear on the alternator &/or water pump bearings & housings, since there is no increased load on them compared to being in a non-A/C set-up (ie: they are both simply being driven by a belt). If the same belt/pulley configuration is used, if the alternator was mounted in the "old" stock location & the compressor was mounted up top, then the alternator (pulley) would have to drive the compressor & the water pump (& the air pump on early cars). That's a bit of a load for those little alternator bearings... Looking at the diagrams below, if you were to simply swap the places of the compressor & alternator (assuming things fit spacially), & retain the same general belt & pulley configuration (ie: crank driving compressor directly using a longer crank-to-compressor belt, with compressor driving alternator & water pump), that might work? The main issues then are most likely how to hang the compressor up there, & how to tension the belt? Yes, the A/C water pump is indeed different (see my reply to Tony's post).