That basic mower was made from 1994-1997, so 10+ years newer than you thought:
1994 (Model 10545, SN 49*******)
1995 (Model 10545, SN 59*******)
1996 (Model 10546, SN 69*******)
1997 (Model 10546, SN 79*******)
Yours being 4.5 HP it should be a 1994 as the 1995-97 should have a "5HP" sticker on them.
One of the most desirable L-B's after the Toro acquisition in that it includes the "F" engine, Cast Deck, and Toro design 3-Speed Transmission, plus it has the optional Electric Start which is nice.
Being from the Toro era, it also has the more reliable top mount pull start recoil set up that was a drastic improvement over the earlier OMC era "F" engines with the vertical recoil.
Doug