Put the new valve into the mounting plate. On this job it was a perfect fit around the plates gasket. If your retrofit feels loose, add a round and a half of black electrical tape tightly around the neck of the valve. If you want to run a "do I need tape" test before bolting the valve in, simply turn the vacuum power unit on, close the lid and listen for a major air leak at the valve. No leak - no tape needed.
It is important that you buy new bolts. The old ones heads are too tall and will not allow the new valve lid to close tightly. We bought one and a quarter inch long by 1/4 inch wide flat head tapered bolts. They worked perfectly.
On a few of the mounting plates we had to move the clip that the bolts screw into further apart from each other. (I think the new valve bolt holes are a little further apart than the old ones were.)
You'll need to screw the 1/4 inch wide bolt into the new plastic valve because the hole was molded for a slightly smaller bolt.
Tighten the bolts down but do not over tighten or the valve will bend and the lid will not seat properly or close straight.