hello everyone,i have a 69 evinrude,33hp ski-twin.starts and runs good.however compression is down to 75 lbs per.cylinder.think about replacing power head.have 2 available,one is a johnson 35 hp,model rds 21b,serial 196644.the other is a rude 35 hp,model e35elcsn,serial e0004130 .the latter is a 1980 something model,will they work as swaps for my original power head?thank you all so much for your help.Janis