Finally done it and started to modify my SDA-1A's into pseudo 4.1TL's whilst waiting for delivery of the new silk tweeters and deciding which tweeter would be better. After looking at the 4.1TL & SRS 3.1TL schematics I must say that the RD0198-1 looks the best bet. I suppose if they used the SL3000 (RD0198-1 replacement) for the SRS3.1TL I gather that it's sensitivity must be higher than the SL2000 (RD0194-1 replacement). Either way, once I finially receive and fit them (xover mod yet to be incorporated) I'll let you all know.
PS - I found a good use for the SL2000 tweeter, remove the magnet and use the plastic frame as a template for making the blanks that cover the old tweeter cutouts.
I am not too worried about the fact that the tweeter sit proud on the baffle as I'll probably place felt around it to reduce edge refractions caused by the tweeter body. If not has anyone got a suggestion what color I should paint these blanks.
Will send more photos as I proceed with this modification.
PSS - I forgot to mention that by placing the tweeter in the middle has made a big difference to the sound, the treble seems more focus now and no more SDA artifacts.