If you don't have the RiverSoftArt morph transfer, the base G3/G8 figures would work, but I'm not sure that they are designed to be exactly the same shape, so the point at which the figures are perfectly aligned might be more difficult to identify. Think I'm going to try it myself this afternoon/evening and make a script to do it if it's more than just those obvious values. I have to confess a quick & dirty pose transfer between the two generations just covers those and seems to work pretty well. There are the two obvious differences, Thigh Side-Side at 6 degrees and Shoulder Bend at 45 degrees, but there may be a couple of others with small values. The resulting pose bone rotations is then the offset value you must add to a G3 pose to make G8F work with it. Then slowly but surely work through the body parts working outwards from the hip posing them until there is no difference to be seen between the versions.

Having done that, take the G8F version, put it into the zero pose. Then put the G3F version into the zero T pose. If you have RiverSoftArt's G3F-G8F morph transfer script, then take a character and transfer it to G8F.

Daz 3d pose