Mating a Top and Bottom Unit

[cprince]

I have a line on two motor halves. I know little about Johnny-Rudes...
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Here is the add for the top end;

1974 Johnson 20 hp Outboard

In good condition but needs the bottom end. Compression very good. Excellent part motor or whoever wants to repair it. Everything else is complete.
$150

I asked him for some detail and he e-mailed me this;

"Serial number is C13000, the bottom part which includes the prop. Everything appears to be there. Compression is over 85 lbs per cylinder."

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And for the bottom end:


Evinrude Johnson 18-25HP lower unit gears, etc. - $100


Lower unit gears, shafts, bearings, etc. for 60's - 70's 18-25HP outboards.

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So... the way I see it, I should be able to get a 20hp Johnson motor for around $200 (I am quite good at haggling!)

What do I need to watch out for... should these units be compatible? What do I need to make this happen? I would imagine that there are gaskets involved... gear oil and the like...

Any suggestions? I have worked on cars all my life... but not OBs.


Thank you all!