I finally got my act together and did exactly this (except 2x6 boards) for two of the bays to get it back open. I think they turned out ok and the depth is 1.5" so it sits flush. There are a lot of other issues that need to addressed but at least it's open.
The pits are 51"x28" so it limits my options since it's an odd size. I've talked to Kleen-Rite about the fiberglass grates and they think I can make 4'x3' grates by adding a 3" strip on one end. A little worried about having support issues, but the lip it sits on is 2" and the vehicles rarely roll over it directly (bays are small) so it may not be an issue.
Thank you all for the help and support. I'm finding my motivation again and realizing that I need to give it more serious attention and not 'mickey-mouse' it with little fixes. Some upgrades are required to breath life back into it.
