Im not sure what you got going on there but 333-3144 is for a Mercury 50 Hp. 500 Lightning Energizer Distributor Housing .Your serial number does show 1968 650.You should have a distributor that looks like this (first Pic)
I found a good deal on two 'parts' motors. One is a 1966 Merc 650, the other a 1969 merc 650.
The 1969 has the same ignition setup as my 1968. 333-3144 distributor and 333-3213 switch box. So now, I'm thinking that the parts are the correct ones, which is good news. But I'm back to square 1 on the tune and sync.
I can set the carb mixture screws for good idle at about 1.5 turns out from lightly seated. Idles well, but bogs down under load. If I set it too rich, I have power, but it idles rough.
I have an abundance of parts now, so I'll try using all the best ones and report back...