Guilty.
The thing is, under LBB2 rules, they'll all be 600Td, J6/2G; most will have 2 turrets. They will also only have fuel for two weeks of power plant operation.
They can't be built smaller than that. At 400Td, a J6 ship is just a big, fast, Xboat. There isn't room for even a 1G LBB2 M-drive, and even then it requires exploiting the Xboat fuel loophole.
And anything much bigger than 600Td can't properly be termed a "courier".
Off-topic insight: While working out a scenario involving a not-quite-derelict ship with "just barely enough" fuel tankage, I figured out why the minimum power plant fuel duration was set at 1 month:
Misjumps.
Misjump duration is 1D weeks, which means that if you only have 1 week of fuel (as is the case with Xboats), 5 times out of 6 a misjump will last longer than you can keep the Jump field running. And then Bad Things Happen. With a month's worth of fuel, your odds go up to 2:1 in your favor that you'll make it through.
J6 under HG-80 at 100 Td TL15
020 Bridge
007 Model/6
006 PP 6
007 JD 6
002 MD 1
006 PP Fuel 4 weeks (1.5 T for 4 weeks
060 JFuel
004 SR x1
totals 112 tons... of which we can shed only 8.5... 2 by switching to a half stateroom, 4.5 by having only the fuel for the week in jump (CT says 1d6 days battery power, so we can get by on that), and 2 by shedding the MD. Can't be built RAW.
Ignoring the roundup requirement of the rules...
we can get an "express boat" type J6 design at 122.
we can get a J6 P6 M1 4 week PP Fuel at 163.5 tons.
With the round up to full ton requirement, Express J6 P6 M0 1Week is 125 Td, and J6 P6 M1 4 Week is 175 Td.
Oh, and the "X-Boat Loophole"? it isn't one under pre-81 editions of CT. It's the standard. Computers can be smaller, too; the programs for Jump take less space, and so a 1/bis can generate and run Jump 6.
Let's see
020 Bridge
001 Model 1/bis (Generate, Maneuver, Jump6)
020 JD C
060 JFuel... Ok, not at 100 Td.
Try 200 Td...
020 Bridge
001 Model 1/bis
035 JD F=2
004 PP A =1
001 MD A=1
120 JFuel
010 PFuel
008 2x SR (P, N, E requ.)
199 Td. 1 Td left for cargo. Valid Bk2-77 design, military crew Double occupancy.
Note that Bk2-81, you can't build it validly until 800 Td... because the X-Boat Exception isn't actually in the construction rules...