I'd say straight up 20 dtons per Starfire space, power wrapped up in a percentage per system that is 'off-chart' and degrades along with system hits.
Maybe use (J) engines as a measure of how much J-drive you have, proportionately. That would yield similar results to LBB2 drive/space/hull concepts.
I think Alkelda Dawn used that letter for special warps, I don't precisely recall.
This makes most weapon systems 60 to 100 ton bay weapons, which does quite a bit to keep a similar alignment of size to weaponry.
So a 100=ton scout works out to something like
HX(J)Q(I)
I would turn Aramis' approach on it's head and since a space is 20 dtons, then a Q space is 5 staterooms, or 10 double occupancy or whatever for barracks.
You're throwing away the whole L-Hyd fuel concept I am assuming, so no need to figure out a conversion for that.
Not quite getting the attraction of vector movement for Starfire ships. One of the things that is 'wrong' is the whole size to top speed issue, where the bigger the ship the slower it can go and the more waddly the turn radius.
Since you are talking foregoing Starfire engines, then I would suggest a 'rules change' to entirely ignore hull to speed limits and turn radii.
Finally, the part that has me concerned is the economics.
In general, you are throwing in an entire ecosystem up against each other that was never developed with compatibility in mind.
Traveller ships in particular do not function in an economic vacuum, there are rates and profits and costs to consider, and even for 'national actors' in both games there is ultimately taxation revenue limiting ship/fleet design.
Assuming one is not throwing over the whole Traveller ecosystem moreso then the L-Hyd economics, then the ships need to have a similar or slightly higher capital cost structure.
The easiest thing to do is perhaps do a series of ACS conversions in Starfire, cost them out, then apply a standard multiplier against them to bring them within a few million credits of the original Traveller costs.
I think just from quick lookups that might be divide by 3, but it greatly depends on which edition you are using.