The assets from the prototype cart could be added to the final bug-fixed version: I mean the level design and tiles. Especially since there are loads of people interested in this particular incomplete demo, because it has some extra levels.
But the ROM needs to be shared for starters publicly for that to even happen. You can see that the work on completing Resident Evil 1.5, Resident Evil GBC, Starfox 2, Earthbound Zero and more recently Mr Nutz 2 and a Lufia prototype only begun when the rare prototype was published... Since it can't really start unless with as much competent programmers/hackers as possible on board. I'm sure with all the Castlevania hacks around there, at least there is someone who'll be interested with what you have and take a look on it.
Since you can't post ROMs here, you could make an ips patch from comparing the official US version (as the original ROM) and the prototype version you have (as the modified file), and simply post the ips patch here. In this case, there are two prototypes so two ips files.