In general, one should look at Stargrunt 2 as well before making a conversion. DS2 and SG2 interlock (SG2's Vehicles are designed with DS2).
Also note: there is a tie in in More Thrust for landing craft in Full Thrust 2: 1 Mass=50CSP; SC*4=CS for vehicles, and 4cs=1 man awake, 1 CS per man frozen..
Soo... that being said, and knowing that Traveller's heaviest tanks run about 20Td, and DS2's run about Size 5... that gives a rough estimate of 4Td per size, and that jives nicely with the descriptions. However, 5Td fits easier with the build system.
Note that 1 element of 4-5 infantrymen is costed at 4 capacity; this is about half the rate of MT/Striker, and Powered armor are double. If trying to recreate imperial craft, I'd suggest using 2 capacity per fireteam instead, and 4 per PA...
Plasma Gun (DFPG): Reduce cost and range by some factor, and the following damage.
At Close: All chits; Red double value.
At Medium: All Chits.
At Long: All CHits at half value
Against infanty: Red Chits only at any range