imo NEVER hammer in the bearing caps of a fresh u joint.

to remove a bad joint the easiest and safest way to eliminate stress on the yoke is to use an angle grinder to slice thru the joint itself leaving the 4 bearing cap remains in the yoke.

then, lightly tap out the bearing cap remains from the yoke while is sits snug in a vise. they come out easily and with little effort

to install a fresh u joint i hand start the bearing caps into the yoke on the both ends.
place the u joint into the yoke
slowly press using a bench vise the bearing caps into the yoke until the joint is no longer able to slide anywhere but further into the bearing caps.

then press slowly evenly until the caps are in.

test your u joint for easy flexibility in both directions before install of the driveshaft into the car.. if needed press one side or the other until easy flexibility is achieved.

all 3 ujoints on a 240 driveshaft at least among the later models (89-93) are the same

personally i install the joint into the shaft itself first and then install the other 2 bearing caps into the tiny flange end. doing it this ways makes it easier to manipulate the much lighter flange end than having to deal with the weight of the shaft.