According to Moss in their TR2-4A catalogue, solid axle TR4As represented
about one fourth of the total production. I owned a 1966 TR4A during the
time the 4As were new, and I can't say I ever say one that wasn't an IRS.
Moss also goes on to state that the CT prefixed solid axle version was
"exclusively for US distribution." However, down in my bone yard, I have a
right hand drive solid axle frame (sans body and engine), that the seller
told me was a 1967 model year car. Jerry Oliver, Olympia, WA.