Other way round.
The articulated Husqvarnas were always called Rider 155 not 155 Rider.
AFAIK they were all made in Europe at the Johnsored factory as they are a copy of their original articulated mower which dates from the 80's.
The parts listing list USA versions as a separate models from the others so their might be an imperial version, don't know all I have seen were metric.
They dumped stacks of them down here & I was told it was because of the instability and law suits from idiots flipping them when turning on side slopes.
The 155 comes as a 2 WD & a 4 WD .
Are you sure it is a 1983 model ?
The ones from that period were named by their deck size in mm and engine Hp eg;- rider 970-12.
One of the few mowers it is a real pleasure , almost a priviledge to work on.
Jacks Small Engines have a parts list for a Rider - 155 ( 2003) and it is the only year.
All of the ones I have worked on used the same spindle & toothed pulleys for the timed blades although there was a regular deck with standard blades.
The spindle is only available as a complete assembly, housing, case bearings & shaft for the timed deck but the plain deck has all the parts available separately.
Which kind of deck do you have ?
They are very unstable when turning on slopey ground and even on flat ground if you try to turn too fast.
They also will not cut long grass so I would call them a fine finishing mower and gives the absolute best cut form any rotary ride on I have ever seen.
I do hope you enjoy it.
http://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/husqvarna/ride-mower
They are listed in computer order so navigate way down the list to the numbers starting with R
Owners manuals and service manuals are available from here
http://www.mymowerparts.com/pdf/
But don't ask me which ones are yours as I downloaded all of them and then changed the file names to a more user friendly one