As far as I know, threadlocker hadn’t been invented yet in 1957. Or if it was, it was not used on that motor. The first time I ever came across it was to keep all those little screws from all falling out of Homelite chain saws.

OMC/BRP Gasket sealer for general gaskets, both sides. You can cheat on brands on this. If your new head gasket has pre-applied sealer on it, don’t add anything else. No goop on intake manifold/reed plate/carburetor.

Hint: To apply the gasket sealer, lay the gasket on a magazine page, and paint it on (like a coat of paint). Flip it over and do the other side. That will give just the right amount. Close up the magazine and save for the next job

EDIT: Apply a generous amount of gasket sealer to the bolt threads too.