Martin-370425

I have recently purchased a DCC Ready R2548 BR 4-6-0 Grange Class [Frankton Grange loco] and bought a Rails 8 pin stay alive decoder. Unfortunately although the decoder is very small it wont fit in the loco. Because of the very limited space the decoder must be the same size as the "blanking plate"or smaller. Can anybody out there advise what make of decoder should be used