That's definitely not a 1991 model Massey 135 tractor.
Judging by the pictures, it's a deluxe and appears to be a 1964-1967 model. The solid red front wheels would normally indicate a later year, but it appears to be an older restoration so the colors may not be accurate. The air filter is the tipoff to it's approximate year range because the vertical-style air filter was only used prior to serial number 641023533, when the newer horizontal-style air filter was put into production. An easy way to remember the air filter "clue" is to keep the year 1967 in mind.
Vertical-style air filter = 1967 or older
Horizontal-style air filter = 1967 or newer
It doesn't appear to have multipower and has been converted to use an alternator instead of the original generator. The hours (46) can't be right considering it's age, and the serial number (897719M2) the ad has listed is actually a part number for a rear axle center housing, but someone who is inexperienced with these tractors probably mistook it to be the serial number.
Lastly, the price ($5500) seems a little high. IMO