My apologies as when i suggested that you go with that plug I was assuming you had a S6S motor at the time? I would go for a roughly 24 tho inch gap and try that. That plug with its inherit heat range, self cleaning capability is mebbe better matched for the S6S motor and a larger carb?
Here is what I found in my own independent study the spark output looked consistently hotter/stronger on the S6T ignition system to me in comparison to the S6S. ignition.
I imagine the plug will work perfectly fine in your S6T model.. The electrode could wear down faster dunno?....
Could P.M.
http://motorbicycling.com/member.php?u=163 and see what he uses on his S6T. With the racing at the tracks he does, will no doubt be a fair polished study.
If you look at the Morini USA sight it does suggest a plug for these motors when reading the model speck's.
http://www.morinifrancousa.com/engines.htm My Stock plug actually did very well on My S6T motor. However NGK is my most favorite plug ever so far. Working in a small engine shop has consistently shown me that no one there likes Champions brand in a weed whacker , blower or lawnmower. We use Denso's and NGK plugs in everything. . Can always cross reference to one of these?