I have several sleds that take the 042 belt but I have 3 new 070's hanging on a nail in the garage . By the service manual,looks like length and width are the same, just the angle on the sides is 28 degrees on the 070 and 32 degrees (or something to that effect) on the 042.
Will the 070's work fine ?
Are the sheaves actually machined different on the clutches or is it just a belt design change ?

Yes, and yes, they changed the side angle to match the sheave angles closer.

I know you already have the 070's, but the '066 top cog works fine as well or re-shim the clutches and I prefer the 075.

for a couple of years now the #070 is what the dealers would send me in replacement for #042.
most sleds will run just fine with it, just check the belt/sheave clearance.

Replacement belt for the the 042 is a 045.
You will lose performance with a 070.

Neither the 042 or 045 is available. Both are replaced by the 070. The 045 was only a closer tolerance version of the 042!

Wrong......The 045 is still available.

Where, I have a couple of older sleds that need them?

Go here and enter belt # into quick parts search.

http://www.babbittsonline.com/pages/parts/...14/default.aspx

I have one brand new 3211045 that I will sell for $35 shipped. U.S. only.

i did notyhing come up the 66 is a much better belt any way

the 066 is a 28 degree belt also.
The 066 is CVT and if used imstead of a 070 application 1-2 gram of drive clutch weight is needed