Given what the Assassin was, and given the coverstock on the Sheer Havoc, their performance should be pretty close overall. Not indentically, given they were made in different oil & ball eras, but I believe the SH should react similarly to the way an Assassin reacts now (without a worn cover, of course). Any changes could probably easily be handled by cover modifications.
Yes, the actual composition of the coverstocks are different, but both are polished particle covers.
Both should handle medium-light to medium+ (maybe as much as medium-heavy) oil of today's quality, depending on hand and drilling.
--------------------
Bowling: Just like hand grenades and horse shoes, you only have to get close.
Life: Deal with what is.