TOOLFORLIFEFAN (Larry) came up with a great solution for anchoring/securing the drivers in several vintage Polk models, mostly consisting of the SDA series. I had him make me a set for my Polk 5B's in addition to a set for my SDA 1C's. He engineered a series of metal rings that fit behind the driver cut outs inside the cabinets with threaded nipples that go through the current screw holes (after enlarging them a bit) and fit flush with the front baffle.
This way instead of using wood screws to secure the drivers to the baffle you use threaded bolts into the threaded nipples. This sandwiches the driver basket between the particle board baffle and the steel ring behind it. No more stripped out wood holes and a much more solid way to secure the drivers to the baffle.
3 or 4 - 1" C-Clamps (most important tool)
I used a 9/32 wood drill bit
Phillips screw driver
Small flat blade screw driver to remove the glue (as necessary)
I've had the rings for awhile and just needed to spend the time to install them. Larry provides templates which you simply secure in place with C-Clamps and then drill out the existing screw holes to accommodate the threaded nipples attached to the rings . The 5B's are smaller so I used 1" c-clamps and they worked perfectly. This was also intended to be a trial run before I jumped in and did my SDA 1C's. This turned out to be much simpler than I had thought. One area that some time needs to be spent on and is a bit of a PITA, is removing the glue inside the cabinet.
In both 5B's there were thick globs of glue around in the inside portion of the PR cut out. If you don't remove the excess glue the rings won't sit flush on the inside of the baffle. I used a small flash light sitting inside the cabinet, a box knife and a small flat blade screw driver to cut and chisel out the excess glue.
One other thing of note is for the MW driver and passive radiator you will probably want to use a washer between the bolt head and basket. The bolt heads are only slightly larger than the basket screw holes and if you don't use washers there is a good possibility the bolt head will "punch" through the basket hole. This is not an issue with the tweeters.
Another tip is once you start tightening the bolts, tighten them in a criss-cross pattern and evenly tighten all bolts. If you don't do it this way, it is very easy to distort the driver basket. Also I've found you don't have to tighten the screws down with an iron fist. Just snug them all down.
I had originally used Mortite in place of my disintegrating original gaskets. The Mortite was completely intact and was not messy at all you'll see in the photos it stayed right where it was supposed to be. Mortite works well and without any issues. Highly recommended.
You can see the rings and templates as well as the tweeter brackets (in the upper left)
All the drivers pulled and you can see how neat a tidy the Mortite is after about a year. No issues with it sticking or pulling away, etc.
Mortite works as intended.
Templates are in place ready to be secured by 1" C-clamps prior to drilling the holes.
Example of the glue issue I mentioned. It's a pain working in such a small area but luckily the glue comes undone pretty easily.
Tweeter bracket in place ready to drill. I drilled out the existing holes for all the drivers.
The bracket has a cut out like the template and to keep the tweeter bracket and driver ring from interfering with each other the ring needs to be installed with the cut facing upward.
It's really simple and straight forward. You need to remove the glue, and for the passive radiator rings Larry provides two scores in the rings where you will need to bend the ring slightly to get into the Passive radiator opening.
Much simpler than I thought. Some will want to use a drill stand to ensure a perfect perpendicular hole, but I just eyeballed it and had zero issues.
I think that covers it. I have just a few hours listening with the new rings, but I do notice some of the fixtures in my office rattle now with low bass notes where they didn't before. I do think there is increased bass that seems to be a tad firmer than before. But I need more time to evaluate other subtle changes.