"Break-in" period was a poor choice of words for me. Perhaps I should have said break-in procedure instead.
My concern (apparently unwarranted) was whether there was any special consideration to the bearings, gears and the U-joint when placing a new or rebuilt 30's era transmission into service.
I'm not going to immediately go our and race the machine, but I do want to give it a good launch.
...took sick over the weekend and had to postpone installation. ;-(
