Hi and welcome.

That would be perfectly fine, just plug into the left (mono) input, and you can use either the left output for mono, or both outputs as the reverb tries to give it some stereo spread.

The fine folks at Alesis still have product information and the manual online for this "Legacy" product.

Thanks very much, I have been told by a friend that I would need a DI box for the guitar, is that right? i thought the signal might be strong enough to use without one

No DI required, just read the manual (which will explain setting optimum levels) and adjust the knobs. It has enough gain to compensate for the relatively low output of a guitar, or it can also handle much hotter line level signals. Knobs are good.

You are an absolute legend, thanks I will read the manual now