pboulanger wrote:Mine is a 1984 DSII.
So you used the smaller holes to bolt down into the pre-existing plate, and then your new block screwed into the larger holes in your adapter? Did you need any sort of backing plate, or was the strength of your adapter enough?
Yes, the smaller holes were countersunk, and I used flush-head bolts (forget the correct term) to attach the adaptor to the existing trunk holes. The larger holes were tapped to accept the base mounting screws. The adapter was aluminum, and I didn't need any other backing plate. I later did away with the adapter and did as John and GL describe, rotating the base 45 degrees and drilling/tapping new holes. I did in fact hit metal, so at least in '79, the plate was large enough to accommodate the bigger spacing. Not sure on an '84, but you could do as GL describes and drill an "exploratory" hole. If you hit metal, great, proceed, if you don't, no real harm done, just go with an adapter.
The plate is glassed in just below the surface of the land on the trunk - if you look/shine a light down into the existing holes you should see a glint of bronze or SS or whatever it's made of.
Here's a pic of the adapter installed
And after I removed it