'78 Delta royale
I haven't gotten around to checking yet ...
If anyone knows:
The 6 x 9's are covered in the trunk with that small insulating 'cover ...
After removing that, will the speakers be able to be removed/drop out from the trunk (hopefully) ... I'd like to replace them but don't want the hassle of having to remove the back dash cover ....

 

They drop into the trunk, no rear deck removal.

6X9 Confirmed.

I have a set of Pioneer 4-Way 6x9's sitting in there now, PLENTY of room.

Very easy to do!!!

 

Now if your stock ones are still in pretty good shape, store them away in case you wish to revert to stock, or sell to someone looking to go back to stock. They would be good for testing old Delco radios, too.
Good originals are getting very hard to find! I am still on the lookout for some good 4x10s for my '86 Cutlass.

 

I have the same car, and I'm also in the process of changing speakers.... I took off the insulation and the bracket but it was still stuck.... I couldn't find any other screws, are they glued in? And how do you get to the front speakers, do I need to pull the dash?