Very nice. I would like to add as the owner of 2 Hubley's and the Monogram Metals 1931 Dual cowl Phaeton and 2 Boatail speedsters and the Speedster Phaeton of 1930. Truthfully, the Monogram kits did not evolve from the Hubleys. They are even in different scales! The Monograms are 1/24th scale. Hubley Packards are 1/22 scale. They are much larger, so I don't believe there are any parts that fit on Hubleys from Monogram. I've built them all.
Your best bet for parts (aside from going to a model show/swap meet) would be to find parts on ebay!
GoodLuck. Looking forward to seeing your build completed. Happy New Year.