The GTROC has an exchange deal where you can get sent a complete set of covers and get them polished/sprayed etc. before fitting them. That way you can continue to use the car while the covers are being done. And it's FREE!
I have read somewhere that RB26 covers can be fitted to a 25 head, but thought you needed a plenum that would suit. i.e. the crossover pipe found on the RB25 won't fit with the taller 26 covers in place.