I currently have a 2230 serial no. 6614 (1972), and it has a screen printed face plate, but has a gold anodized chassis (rather than silver chassis) ... like many gold chassis I've seen with engraved face plates on early 2270's (have an engraved face plate 2270 now)
A number of years ago, maybe 15 ?, I had what I thought was a 2270 prototype. It had the engraved face plate, and other differences inside, not seen on later 2270's. I don't recall what they all were, but one thing was a multi voltage bank along the back, plus other things.
Just too long ago, and too many others in between to remember.
The biggest thing that made me think it was a very early prototype, was it had a serial number plate on the back panel, but no actual serial numbers at all. Only Marantz I ever saw like it of any model. (had 100's of Marantz units over the years)
At that point in time I was buying/selling/servicing Marantz receivers about as fast as I could turn them over. Engraved face plate receivers were not so "collectible" then...had a bunch of them. Usually had maybe 5-10 2270's constantly, so sold it to someone in Minn. as I recall.
...big mistake as it turns out now.