Shermaniac
I agree with KirbyClassicIII, either a 510, 511, or 512. On the bottom of the unit, there (originally) was a serial number tag that would also indicate the model... is that still intact and legible? Regardless, it will still be a lot of fun to get it back to its original glory. These kinds of projects are always a blast... your grandson is very lucky. You two have a really awesome project in the works. I think this is awesome. Keep us posted on the progress, and if I come across anything that may help, I’ll let you know!