Those block dont like to be overheated as the aluminum will pull away from cylinder liner . This causes head gasket to leak compression into the cooling area, which as RPM increase the pressure will overcome the impeller flow.
Here is link to look up parts. CDI pack is NLA from Mercury.. Make sure you test everything under flywheel as Yammy style packs rarely fail
MARINER : 40 (TWIN CARB) (W/OIL INJECTION) : 6E9-150001 AND UP (E) | PerfProTech.com