i obviously missed something...

whats this 7" thing? is it the size... of what?

it relates to the size (diameter) of the cwp but is also the measurement across the top bolt mounts..

Ned.

so my simple common knowledge tells me only a 7" one fits a locost? or is the best fit?

7" is normaly best as is smaller, lighter and the same ratio's are available afaik. some manufacturers make the dif mounts wider so you can fit both, a 7" just needs a 1/2" sleeve/adapter/spacer in these circumstances..

Ned.