Firstly I'm sorry to hear of the passing of your husband, do you know what his name was on here?
Strangely only a day or 2 ago I was looking at something on the internet and I saw a machine that looked exactly the same as this one the topper/display board is not original but it nicely finishes off the machine as a single cab
Have you tried plugging in and switching on at all? to be honest with a mame fitted machine it's not really a massive issue with it working fully, if it powers on and the screen works depending what screen is fitted, CRT or LCD will be factor for many, also depends what sort of conversion was done, we could possibly find threads on what he had done with the internals to get an idea that way or if someone on here is local to you they could pop round to have a look at what specs the machine is to help with sale, if I was close I'd happily take a look to help out
Regards
Chris