Possibly the easiest is the job I did a few months ago with the Melody figure from RDNA. That has an animal head on an A3 body, with modified hip geometry for a tail. Which makes some Aiko add-on morphs awkward because of the changed hip.

Little_Dragon provides a very good add-on tail as a freebie, so I decided to combine the standard A3 body with the Melody head and neck.

No need to make bridging geometry, just combining the bits from the two figures. There are some complications with different names for the morph channels used in INJ poses. Frankly, a huge amount of .cr2 hacking.

Note that the full version of A3 is currently available for free from DAZ, as part of a bundle. I think one bundle has just the LE version, and another has the full version.

Another example of a head-transplant is Little_Dragon's Millenium Catwoman, which puts the Millenium Cat head onto the V2 body (you need to have both the original figures to unlock the encrypted model data on that, and I think DAZ have a lot of old stuff on sale).

Finally, one quick and dirty trick:

Pose the donor head/neck with the morphs and eye positions you want.

Export just the head, neck, and eyes as a .obj file.

New file with the figure you want to attach the head to. Import that .obj and it's now a prop. Position relative to the new body, and save as a smartprop, parented to the target model.

Slightly blurred memory suggests that some versions of Poser have features which automate some of this prop-as-bodypart stuff.