Okay this is confusing. Clicked on the Sierra, $536. Searched for "318 electronic distributors" on Amazon and got a lot. Prices ranging from $50 to $600. Looked at a few but saw no mention of VR. Did see M in a few of the part numbers.
Back when Mallory was still a Mallory company, they had begun phasing out the YLM ( YLM = VR = variable reluctor ) in lieu of the YLU ( photo eye ) units.
This was a "shot in the foot" in my opinion. VR is trouble free and always has been!
I do see some vendors stating that the Sierra unit is a direct replacement for the YLM series, but it is NOT!
They are apparently substituting with the YLU!
So do these auto distributors (LA) work on the marine LM?
The automotive advance curve is incorrect for Marine use and could lead to engine damage!
The automotive units are NOT ignition source protected.
Vacuum advance is ineffective for the Marine engine and is not USCG approved.
At what price range do they become junk? I have a '71 LM 318 with points.
Prices on the new electric systems have become outrageous.
If you are willing to routinely replace the contact points and are good at adjusting your dwell angle, you will be OK until you find a good price on the unit that you want.
Thanks, Friz