Many 760's had a Yazaki cluster, while most 740's have a VDO cluster. You can tell the difference on how the tripometer is set up. On VDO the miles are together, the tenths are separate. On Yazaki, all four numbers are separate. Also, many 760's had ABS, while most earlier 740's did not. If so, this means the sensor in the rear end is different. I don't think the speedometer will be far enough off to warrant the change if the instrument panels are different. I drive a 1982 245 that used to be a diesel. The first three letters are DIE, and that is what it did. Luckily, one of our customers wrecked a 1984 240, and anything and everything but the rear end moved over to "Abbie". Therefore, I say she is an 84. I still have the diesel rear end. Her transmission has been swapped with a 91 240 keeping her tailshaft housing. I have 15" 240 turbo wheels on her. Her speedo is not off at all at lower speeds, but at 80mph, I'm really doing 90mph. If all of these changes only affected a change of 0-10mph, your's should be even less.