The way we do 16 or 18fps to 24fps is a little backward but it works, starting with a 16MM film shot at 18fps, we run it thru the converter witch only runs at 24fps , the 1st copy S-VHS tape is now 6 fps to fast, the next step is to go between 2 vcrs. By using the edit function we slow the playback deck down, , then when the 2nd deck (running at normal speed) records the feed from the 1st deck ,things come out fairly close.
Did do some super8 for a local modeler , we started with a vhs tape ( overspeed ) that he had made, we got it slowed back down for him, it came out alright.
The decks we use with the ELMO coneversion unit are Panasonic's AG-7300's and AG-1980's.
Its not the best system, but its a lot cheaper then going with a pro-editing house and Rank Cintel equipment.
Have also taken the audio part of films and ran them thru the Reel to Reel decks in the studio and adjusted the speed with the tape decks controls, then dubbed the audio back onto SVHS or VHS tapes.
Hope this didn't bore you to much, if you come up with a overspeed tape from your super8 and wan't to send it along , I'd give it a shot at adjusting the speed for you. John