289 progress........

[HealeyRick]

There were about 640 factory built 100Ms that featured larger carbs, different cam, high compression pistons, a cold air box for the carbs and a louvered bonnet with bonnet strap. These cars are well documented. There were also 500 LeMans Conversion kits, that were used by dealers and private owners to convert their cars to M Specs, generally without the high compression pistons. These are properly known as "LeMans" cars and not 100Ms. There are very few documented in-period LeMans cars and they are worth considerably less than the 100Ms. Finally, there have been lots of later LeMans conversions, even to this very day.
Because the 100M is so valuable, a good one sells in the $200k range, there has been significant misrepresentation of these cars, both purposely and accidentally. Anyone planning to buy one now really needs to talk to a 100M expert first.
And as Larry says, the one to have is the 100S, a factory race car of which 50 were made. They change hands in the $2-3 million atmosphere. One of the greatest experiences in my Healey life was driving this one originally owned and raced by actor Jackie Cooper