|S4LN-20 does not have impulse coupling. S4LN-21 does have impulse coupling.|
TCM NEW MAGNETOS S4LN 20(RH) /S4LN (LH)
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You are correct, only S4LN-21 has an impulse coupling. S4LN-20 does not.
Yes, these are new units priced as each.
Both mags are LEFT rotation, LH and RH are referring to which side of the engine they are installed.