When on land take out one threaded stud at a time and replace it with a
stainless steel hexhead bolt with large washer. This has worked for more than five years on my 1970 MKII.

For anyone curious, was able to clear away the corroded nuts/washers/mounting plates (a power grinder is a wonderful thing). Thankfully, the studs were solid and threads sound.

I drilled 5 new holes in which I tapped and thredded new bolts along with s steel plates and it seems to be working fine. I didn't have to drop the keel. I you do drop your keel would you be so kind as to take some pics and email them to me. Thanks.