[rsk289]

This clip shows the differences quite clearly.
There was a 'TR3B' produced briefly for the US market as an interim between the 3A and the 4, which may be where the confusion is coming from.
However the TR3 runners shown in this clip are nothing like Cobra ones. The early TR4 which he shows us are very close, but not long enough. If these could be modified to fit the chassis supports they would look very good, with a pair of Bakelite Leveroll knobs on the ends.

[ame]https://www.youtube.com/watch?v=Ccy96PbgJ0k[/ame]

In the frozen frame at the start, TR3 are in the middle with early TR4 below. Very similar to correct Cobra.