Bill, the Airfix 1/48th scale Canberra B2 kit I think might have been modelled on the T4, as the kit canopy is incorrect for the B2. It has the circular 'clear vision' panel on each side, which was fitted to the T4 but not the B2.
Basically, all you'd need to do would be to bring forward one of the rear ejection seats, add a few bits, and paint in a 'trainer' colour scheme, for it to look like the T4.
OK, there were systems and other differences but, externally, apart from the odd antenna here and there, the conversion would be as simple as that.
I was quite surprised, in reviews when the kit was first released, that the canopy 'fault' didn't seem to be noticed, as the starboard clear view panel will need to be removed, and the canopy polished, to make the bomber version as intended for the kit.
EDIT: Prem, the Revell P-39 is a new tool, also boxed by ... darn, I forget who the other people are! It's had very good reviews too.
Edit edit: I think the 'other' P-39 boxing may be Special Hobby ? I know the Revell version is quite a bit cheaper though.