Problems w ~ 51 flathead in 46 Mercury Woodie

[Carlsoncg]

Bought 46 Merc Woodie. Finally determined
That I have 51 engine (or at least 49153 engine -bolt on bell housing). Had throw out bearing that rattled w clutch depressed. So took to my mechanic to change bearing clutch pressure plate and disc and pilot bearing. The replacement 38-48 10” clutch parts would not bolt up to flywheel. Ordered 9.5” 49-53 cluth parts
. Reassembled car and same rattle. Mechanic says it has probably rattled since 51 motor was installed. He says either live with it or drill the fly wheel to fit the 10” 38-48 clutch.
What do you think?