That's an odd bird indeed, week 31 is well into 1990. Do you have more pictures of it?
Yeah, I thought that I remember it was produced for a little over a year's timeframe but don't remember where I heard that.
I purchased it recently and everything on it is identical to the 50 Special that I bought new in 1989. The head is 45mm and is original Husqvarna. It's missing the Anniversary sticker on the side of the cover and that makes sense since it was built in 90 and not 89.
As far as photos, it's in pieces right now as I am rebuilding it. I will look in my cell phone and see what pics I have of it as I was tearing it down.