The G3 body is slightly smaller than the G1. People who Customise clothing for both sizes can tell you this. Hats & tiaras are transferable as the heads are similar-sized. I recently restarted knitting Pony capes & the G3-sized ones I make slightly smaller than the G1 ones (about 4/5 size). Pink Kittywinks, who makes dresses for both G1 & G3 Ponies, can also tell you this