Poor Condition Charles I Half Crown Restoration For Display

Hi all,

I have this coin which has a large amount of wear, and considerable environmental deposits. I'm looking for some help on getting it into best shape to display. I could have posted in the general coin sub forum but thought here might be best.
I don't believe the coin is of significant value. I believe it to be from the Exeter mint which has a fascinating history but it's condition goes against it. It was found with the obverse covered in sand which was bonded to the coin by some super hard substrate, almost like calcium carbonate. I tried six months in acetone but after no major change I began to use a composite pen to remove some of the heavier deposits.
I would like to get it to a stage where we can display it but I also am slow to go further mechanically in case I lose any underlying details. I would be glad of any advice. I don't intend to do much with the reverse, just cotton swaps and acetone to remove as much of the compacted muck that still needs to come off, but the obverse is not in any state to display. Could anyone recommend any other types of solution to soak it in that won't damage the coin.

Many thanks,
Flint.