Don't give up yet ! untill you've done a full tune up and valve adjustment , I always hear
" yes, I checked the valves " ~ B.S. ! every one I work on has tight valves and so won't run correctly .

It only takes a couple hours to adjust the valves then set dwell & timing , even with 60 # compression these old things run pretty well .

' Blue Chip ' forklift eh > musta been mighty expensive when new , most forklifts i;ve ever seen had four banger flatheads . or is it just BIG ? .

-Nate
There is no problem so difficult it cannot be overcome by generous application of brute force & ignorance