My customers have a 944 with a blown engine and my customers want something with a little more power Cummins INLINE 6. My customers want to see if a boxster or 911 engine will fit into it or even gm's ls series motors can you help?

 

Anything can be made to work with enough money

Consider that the 944 is an inline 4, water cooled engine - meaning long and narrow, requiring a radiator
911 engines are horizontal 6 engines, flat and wide, air or water cooled - without extreme modifications getting this to work will be almost impossible
LS engine - V8 - longer, wider, seems to be the go to engine for swaps, massive power, affordable, lots of accessories for swap kits, changes the porsche into a camaro -
How about modding the existing engine?
Could be easier and cheaper then any swap, retain the driving balance of the 944
Old sailing saying:
Nothing goes upwind like money