Not a good idea, far in excess from recommended oversizes. You can bore it out to at least 040" safely and install a 3.1 crank and appropriate cast-iron-head 3.1 pistons. You'd end up with something around a 3.2.

With the 3.4 HT crate motor's cam, valve springs & retainers, plus 1.6:1 roller-tipped rockers, Holley Big-Bore/GM 4.3 TBI and bored intake, it should be a very strong runner.

There is a company that touts a 2.8 block overbored to 3.4 specs, but at that point the cylinder walls are so thin that they have to sonically test each block for thin spots. The 3.4 block is a lot stronger than a 2.8 and a better platform for performance mods.

BTW the 3.4's heads are the same as what's used on the Trooper 2.8 or Rodeo 3.1. Typically with casting #'s that end in "884". Some gains can be made by port-matching the intake manifold to the heads, but don't mess with the "vane" in each intake port.

You can turn the 2.8 into quite a revver with performance bolt-ons, but what you're really looking for is more low-to-midrange torque, and the largest gains are going to be made by using the 'stroker' crank.

Check out this article if you haven't already:

http://www.4x4wire.com/tech/60degreeV6/?

HTH.........ed