The HW 90K which I have is not so long,yes it is heavy but that makes it so accurate,I believe from what I was told by Theoben that they never made the TB90,it is a restocked HW90 which Theoben marketed.
The original 90s were all marked with the Thoeben name,I have a feeling that like all HW they are now not that good and may I believe use the car type gas ram.