240d/300d gear ratio

[kchristopher]

I just put an '80 300d motor in my 240d. I'm guessing gear ratios are different for the 240's, since the motor seems to screaming. (I never drove the 240, bought it with a blown motor. My only point of reference is the 300d I bought for the motor, but I did drive it ~100 miles.) Should I be concerned with the 5 cyl. bolted up to the lower gears? I'd like to think I could drive at 75 for a few hours without worry, but still have time to swap the rear from the 300d car if I need to.

Thanks much.