Doubt it because the RS 2000 was only homologated after 75, after they stopped the RS1800 and if you're looking for genuine cars then I don't think it would comply. As to aftermarket heads, I thought the cars could run modified heads but of original manufacture. (I stand to be corrected on both these points.).
All a bit of a shame really because I could have entered the Capri had it been made clear that modifications to the App J regs would be permitted.
Edit: According to
http://touringcarracing.net/Pages/1975%20Cars.html the Zakspeed MkII Escorts were still running the BDA in 1975.