These are all different voltage coils? GT40T coils are 12v, GT40R and GT40RT are 6v/9v(one or the other, I can't remember?)
And I thought the GT40 and GT40T were both 3ohm coils and the GT40R and GT40RT were 1.5ohm coils?
I've been running a GT40, the oil filled type, with an electronic distributor for ages without any problems.
Though I've heard the GT40T, the resin filled type, can be unreliable. Just what I've heard, I've never actually used one.