I have a 1-ton out back that has a GM 14-bolt rear under it with 3.70 gears (if memory serves). The guy I got it from said the 216 wouldn't pull it any longer once he changed the rear.
Granted 3.70 and 4.10 are different, but his experience does confirm it could be a problem. Please come back here and tell us how it goes after the swap!
By engine work do you mean on the 216 or maybe swapping for a 261? Few would ever notice that swap looking under the hood, but I'm sure you'd notice hauling a load or climbing a hill.
