Fuel injected versions of the R-3350 were the -57, -57A, -59 and -59A. Injection was into each individual cylinder combustion chamber. Two injection pumps with each pump servicing one row of cylinders. Used on B-29, B-32, C-97, C-121. Don't have a list of civil applications to hand, though seeing it was used on the 121 and 97 you would imagine it may have been. Airlines may well have had their own reasons for staying away from the technology at the time, if indeed that was the case, eg mechanics not familiar, maintenance issue etc.
Edited to add: found a TCDS
TCDS E-272 Rev 9 Curtiss-Wright/Marquette, Inc. for the civil fuel injected R-3350. Fitted to the turbo compounds as 411A mentions. Some non turbo engines had fuel injection also.
TCDS E-218 Rev 12 Curtiss-Wright/Marquette, Inc.