compression

Having trouble starting a Yanmar 240D. Used it and parked it. Now getting lots of white smoke but doesn't even make a pop even with a block heater making it warm. Last try I decided to adjust the valves and I was able to put a 8" wrench on one of the front pulley nuts and turn the crank fairly...

I broke down and bought a compression tester for my s370 w ke70 diesel. I. Getting 300 on front cyl and 280 on rear. Thats cold, tractor wont start below 60 deg even with heater. I've read diesels need at least 350 to start but was told 350 was good for a new moter at 6500 ft. Whats what?