Looking to install the JL 8" IB4 Free Air Subs, just wondering is the 10" will fit as well without having to cut anything? thanks

Depends on what you want them to fit.

Sixto
95 S420
87 300SDL

Sorry for not been more specific

i want to replace the rear deck speakers on a 99 CLK 430 with the JL free air subs, i will also replace the other speakers as well as the deck. thanks.

Convertable or hard top.

Hard top:
It all depends on the openings in the rear deck steel
the more room, no cutting.
The less room, cutting is involved.
You'll also have to built a parcel shelf cover because
the OE grilles might not fit over the 8" subs.

Convertable:
If you have the room for a box for a 10" then go for it.

Louis.