If you can hook up a TB, you should be able to hook up a spinner, as both (
usually) use the same quadrature signal. (I'm assuming standard arcade TB's and spinners, not ones with special boards.)
Again, if the hacked mame can see the TB, a spinner should work, but

The question is whether a TB & a spinner can be hooked up at the same time (as Cheffo's hint at two headers
might mean), or if a switch is needed and both the spinner and TB needs to be wired to the same header.
Let us know how it turns out.