the engine was built in 1984. I think that the blade length is an indicator of model. Possibly a 9" is a 100 and a 10" is a 200?

Agree with Tom. Engine is 1984 and edger is probably similar vintage.

In those days (1960's though 1980's) McLane basically had two or three models. At the bottom was the 100, which had 6" steel ball bearing wheels. Was usually fitted with Briggs 60102 2hp engine with vacu-jet or suction carb (small tank below carburetor). Next in line (don't know model #) used the same frame, but 7" steel ball bearing wheels. Engines included Briggs 80302 3hp, Honda G150 3.5hp, Kohler K91 and others. Last one was model 800 which had a different frame (engine sat lower) and 8" wheels, again steel with ball bearings. Usual engine was Briggs 80202 3hp with pulsa-jet carb (large tank below carburetor).

Some time in the 1990's McLane starter to replace steel wheels with plastic and made other changes. Current offering is the 101, now with 7" plastic ball bearing wheels, the 137, which is same as 101 but "dumbed down" to only 3 wheels, and the 801, which is the 800 updated to 8" plastic wheels. Obviously engines have changed over the years. Your flat head Briggs is now pretty much obsolete and replaced by OHV Briggs and Honda motors.

Your engine is still a perfectly good one, however. Parts are still available, and if you maintain it properly it should continue to give many years more service.