My 629-2 MR measures 1.702.
A friend has my 6" 629-1 so no data for that one for now.
The old countersunk cylinders are going to be longer but that doesn't necessarily mean they have any more room for COAL.
Seems as if there is some variation between various vintages of 29 and 629 models.
Don't forget the rim thickness. 44 rims are typically around .06".
Subtract that from your COAL to compare to the cylinder length if not a countersunk cylinder.
This means my cylinder above SHOULD take a cartridge 1.762" long.
Your 1.71" should be fine.
Only way to really tell is to load one in the cylinder and see if it sticks out the end.