Jim: Just looked at the book 150 Years of IH. These don't seem to have model numbers. The Deering Ideal mower was introduced in 1893 only 3.5' and 4' sizes, then he lists an Ideal Gaint 6' , which ended in 1911. New Ideal mowers were introduced in 1905 and New Ideal Giant in 1906. These were available in 4.5, 5, 6, and 7 foot szes. This ran until 1910. In 1909 New Ideal mowers type B were introduced and produced until 1918. This type B just seems to be improved versions of New Ideal and New Ideal Giant. The Giant models had heavier gears, wider wheels and I would gather the ones with 6 and 7 foot bars.
He also states that Deering mowers had the least side draft of any mower on the market. My dad mowed with horses and can remember he and fellow farmers discussing the effects of side draft on a team of horses. Apparently side draft could play a team out quite fast. Is also one of the few jobs where I remember my dad resting the horses. That was the reason the old timers kept the big shade trees in middle of fields, The rest areas.