I have extensive experience with the C64. I was the president of our local Commodore club for several back in the mid '80s. I gutted my c64 and metacompiled a FORTH from hand entered assembly listings and burned into an eprom in place of the basic. I took the keyboard interface off and turned it into a SCSI (actually SASI at the time) and used it to access a industry standard hard disk and floppy which boosted the disk i/o speed to 17,000 bytes/second (rather than the 300bps it came stock with). I built a small daughter board having 4 14 pin chips on it that also gave me industry standard hardware 19.2 kbaud RS232 (vs. the flaky 1200 kbaud software serial that came stock with the Commodore).
If feasible, I can give you comparable if not superior than assembly performance with FORTH plus greatly accelerated production time (generally 6-10 times that of most other "production" languages).
I also am a published author in the FORTH community and have computer tutorial web site that features 6502, FORTH, C, digital electronics, etc... lessons. I'm not sure I'm authorized to show them to you here because it would reveal my contact info outside of freelancer.com.
Thanks for your consideration of my application.