Finally the big day arrived. The ripping turned out to have been a tad generous, erring on the side of caution, knowing I could always rip them again but close enough that I'd be afraid to. A lump hammer and block coaxed them into position, but the first one was like playing Whack-a-mole as the previous slats jumped up out of their slots. The clamping seen here, on the second grate, helped that.
If this had been a bigger grate the ripping would have to be looser. A too-tight fit on a larger grate causes them to belly and split here and there. Don't ask.
There's a blob of PL Premium in each lap, which should do the job. There's very little squeeze out to deal with.