Cutting the tap root won't kill the tree, but it may invite decay that over the course of time, could rot the tree from the center (could take 15-20 years or more)
Along with many other fine companies, give Davey a call. National Shade out of Houston merged with Davey a few years ago and have done many succesful and high profile moves as well as Joe Blow wanting this 3 inch oak moved from this side of his yard to that side.
http://www.davey.com/cgi-bin/displayCon ... ion&id=472
1-877-605-TREE (8733)
The fact that these trees are 35 does however present a monetary problem. They may not be able to use a tree spade for that. If they have to bring in heavy equipment, that is $$$. But if you don't call, you won't know.