In the GURPS Vehicle design system (and by extension The GURPS Traveller Modular Design System) Reactionless Drives are said to have "vectored thrust" engines. GURPS Vehicles defines a vectored thrust engine as a "reationless thruster ..(that)...can be modified with the vectored thrust option. This enables ... the engine's exhaust to tilt, vectoring a portion of the thrust downward. It can then divide thrust between lift and forward thrust."
While this gives spacecraft performance equivalent to other forms of Traveller it does not lend itself to the physical ship designs that are considered standard in Classic Traveller. So I've taken the Modules rules from GURPS Traveller p.156 to heart. It says, "Component modules do not have any structural weight or cost - they should not be though of as actual homogenous systems...but rather as sets of components some of which might be scattered throughout a vessel."
So instead of single engines which physically tilt In My Traveller Universe (IMTU) I assume an engine that can thrust in any direction. Most ships also have a number of auxiliary systems to allow for precise tilt and yaw control. A separate system of small reactionless engines equivalent to the attitude engines on twenty-first century spacecraft allow for fine steering during docking and on landing. Combined with contragrav this gives a reasonable propulsions system that should allow the published performance necessary for Traveller vessels. This explaination more or less matches reactionless thruster operation as explained in DGP's Starship Operator's Manual.