The plot thickens!
The Magna name was used for the F and L type MGs and the K and N types were called Magnettes.
I thought I knew that the Eyston/Gardner EX135 was originally a K3 Magnette and have spent some time trying to find a reference. What I did find was Wilson McComb's Profile on the K3 in which he states that
"The car that Eyston drove into third place in the Mannin beg was built of 'K3' components but featured an offset transmission line, and could be fitted with a road racing or track body as required. Known variously as EX.135, the Magic Magnette or the Humbug (because of the brown and cream striped track body) it was destined for a long and honourable career as a record breaker . . . "
The MMM Register of the MG Car Club refer to it by its chassis number, K3023 - i.e. no. 23 of the K3 series.
I cannot argue that it was never called Magic Magna, but can't see why it would have been.
