I had a good look over this machine this afternoon. It is in fact manufactured by Kinshofer, but has several stickers on it stating that it is supplied by GOS as an importer. It is a twin sleeper tamper.
This machine appears to have something of an identity crisis. It appears to be self-propelled yet has no driving position so I assume it is remote controlled when working. Although the RIV number is in the small tamper range, unlike others in this range it has a tow bar stowed with it and notably carries an EAC date (24/08/2023). In reality therefore its more akin to a braked attachment or even a trailer and I assume it is towed to/from worksites by an RRV.
No it looks the same as the April 2014 photo, only a little more uncared for. It looked like bits of pipe work is hanging underneath it. I had a right good look for the rail wheels, but they did not jump out at me.
This entry appears to have conflated two different vehicles, the early 79200 Speno grinder set 555A with this much later vehicle. This is based on some info on 555A from elsewhere - not a set I recorded for myself so apologies if incorrect.
We record previous owners in the notes so the McCulloch search brings up one example but if you did a search for Balfour Beatty you would get many more results as this lists anything previously owned or on hire to them.
As Vince says the fleet lists give current fleet - but sure you know that by now!