Have a D-50 4x4. Replaced the original head with a 2.6l head from a 1982 d-50. Everything matches up except the lower row of bolts on intake and solved that problem with large washers on the studs. I did notice the head from the 82 appears to be cut not as deep around the compression area around the valves as the original. My problem is twofold, I get predetonation at speeds above 45 mph with considerable loss of power when valves pinging. It starts and revs up normally when in park, but when you put it in gear it will not rev up even at wideopen throttle and doesn't have power to pull itself up a small incline. Tried adjusting the timing with very little or no improvement. Have now tore down the head due to blown gasket between the two inter cyclinders. Is my problem with compression or the carb.? It has the stock carb. on it. Someone told me that the carb. was running lean would cause predetonation. Is this possible? It appears to me that the mfg. made the 82 head with more metal in the compression area around the valves when compared with the later model. It looks like the 88 head has been machined out more and removed too much metal around the water jacket area. Could this be what makes the later model head crack so easily? How much do you think this would change the compression ratio? Your help and opinion much appreciated. Thanks