I think the Kennedy, a cruiser in 2300 comes out at around 1,000 displacement tons in Traveller, the size of an escort. Of course originally 1,200 displacement tons would give you the Kinunir class which was originally rated as a battlecruiser. No CG would not be a problem apart from requiring different types of deckplans. The biggest problem I could see was the great range of sensors and energy weapons. You could drop gravitic focussing on lasers but the PAs would still have a very long range. I thought of using the same range formula for both with an additional range penalty modifier for PAs which is what non Traveller GURPS does.