Did some quick checking and found that the F163 puts out about 20 HP at 1500 rpm. 162 Cu In with a 7.4:1 compression ratio. The 135 is 124 Cu In with a 6.07:1 compression ratio. Less horsepower, I'm guessing about 10. The Continental F series used a common block If the forklift is a Clark, they had oddball blocks and they are set up for a hydraulic pump. The F163 probably has an updraft carb and governor. "If" the blocks measure up the same at the connection and you can swap over the governor, it might work but again, less horsepower. There is a website with additional information, Google Bills Welder Repair. Another resource might be the multi cylinder stationary engine forum in SmokStak. Hope all this helps.