I didn't think it would be possible since they're both Origin models, but I was able to recreate it without any modifications. HG 1/144 Char's Zaku II (Origin) + HG 1/144 High Mobility Zaku II (Gaia/Mash's) = Char's High Mobility Zaku II
*It would be perfect with some painting, but I don't have the time.
It's hard to find these restocks or purchases on Premium Bandai, so if you have these two, you can put them together. However, I think there aren't many Origin models being restocked...

CHAR AZNABLE'S & BLACK TRI-STARS (The Origin) | TAZYA's Gunpla works