Huh? Shocks don't apply "tension" at all, except for a little from the gas pressure inside. They dampen movement.

You can gain a little suspension travel by getting longer shocks, especially on the back axle, but you would only see the benefit of that off-road. Really, a t-bar crank and taller coils don't change the suspension travel at all, they just adjust the resting height upward in the same travel range. So you can use stock shock sizes just fine.

It is worth noting that OME makes excellent shocks that are a little longer than stock, and are designed specifically to work with the OME coils. They aren't cheap, but are probably the best shocks I have ever had, and are very rugged.