1963 Johnson 3 Hp conversion to long shaft

Hi-
I'm restoring a 1963 Johnson 3 hp JW18; and converting it to a long shaft. I have the conversion parts (water tube, longer drive shaft, exhaust housing extension). During re-assembly, I am wondering if there is some sort of sealer necessary (and what type) at the follwoing locations:

1) water pump plate to gearcase housing
2) water pump impeller housing to water pump plate
3) gear case housing to exhaust housing extension
4) exhaust housing extension to exhaust housing
5) Exhaust housing to power head (I know there is a gasket needed, but any sealant also required?

I have the service manuals, but they do not mention anything about sealing these areas. Any guidance on these questions (and the conversion) would be greatly appreciated.

Thank you.

1- 3M 847
2- " " """
3- None required
4- "" "" "" "" ""
5- OMC Gasket sealing compound or Permatex # 3.

Boobie- Thanks so much for the response. I greatly appreciate the knowledge you and others so willingly share on thsi forum.