Maybe, though I honestly can't think of how you could get the panels to work as his legs without him ending up with elephant feet. I'd honestly just settle for a purple alt-mode and a really good robot mode.
Then again, someone managed to make PRiDE Vehicon, so it's possibly possible.

Trumpets would be sweet, but six of them would be a bit much to ask from a Hasbro/Takara-Tomy MP figure - especially if you wanted pre- and post-blasted versions. If you're going to do them as a custom I'd suggest scaling them for Hercules or one of the other 3rd party not-Constructicon sets rather than the smaller official Constructicon sets.