I'm thinking of a 6.5-06 build on a long action 700. I have a ton of .270win brass. Anything special I need to know about necking it down to the proper specs?

Other than neck length nope. The 6.5-06 is 2.49+ like the 30-06. The 270 is 2.54ish. LOL to lazy to look up the exact. When you neck down the neck will get longer. So just run the 270s in yoyur 6.5-06 die and trim you should be good to go.

I don't know about the 6.5-06 but I have made a couple dozen 25-06 cases out of 270 brass that I find. Its very easy.

270 brass will certainly need to be trimmed. That and running it through the sizing die to get the proper neck size is all that is necessary. As Paul said, 270 brass is longer. I have used it to make my 6.5-06AI cases.

I just ran a bunch of 25-06 through the sizer die on mine.

I sold off my Brno ZKK600 6.5-06 earlier this year but you can just seat a boat-tail 6.5 bullet in 25-06 cases and go shoot. I did not bother using 270W cases as they will definitely need trimming but I did use 30-06 cases where it is a simple matter to run the cases into the 6.5-06 FL die, load up hunting loads and go shoot, no trimming or neck turning (thinning) needed.

I did find I got slightly better accuracy when using 30-06 cases, possibly because they fitted the chamber better in the neck area.

We have built a number of rifles for this caliber, and have used any available cases.

25-06 Remington, 270 Winchester, 280 Remington and 30-06 Springfield.

With some make of brass, some neck turning was required, and I think in most cases cases needed to be trimmed to a certain degree.