If it has a T-shank Rapido coupler one can probably install a Unimate.
If it doesn't the Unimate can still be installed, but it's more work. Cut the T portion off, leaving just the shank, drill vertical holes through the pilot beam and shank, and attach it with a pin. No centering spring, but it won't couple automatically anyway, so it doesn't matter. You may have to add shims, or thin the shank, depending on the existing draft gear/mounting holes, but that's basic kitbashing. If you don't want it to pivot, it can be glued in place, but I'd still use the pin for strength.
I've never had a Spectrum 2-8-0, so don't know what would actually be required, but I did a similar conversion on dummy F unit many years ago. It was easier to use the body-mount Unimate, but I didn't have one at the time, and the converted T-shank coupled closer anyway.
