I made a set out of pressure treated 4x4. Cut them down, drilled the holes in the center and soaked them in a can of sanding sealer. They worked just fine and will probably be there after the bed rusts off of the truck for the second time! I thought the offset washers were to keep the main bed bolts from turning and pulling through the wood.?? Does anyone have a template for the position of those holes?
I'm seeing the same problem with 2-1/4 blocks with an addition of the thickness of the rubber spacer pushes the rear sill mount about 3/8" in the air. This does not seem right. Any body have a clue as to why the blocks are cut too thick. I do not want to torque the bed down and stress the side bed panels. Just for the record this is a 36K original miler with original sheet metal never hit and the frame is straight as a pin too. Bluemeane might be right the spacer blocks and rubber spacer should equal 2-1/8" combined to eliminate the gap at the rear sill.
The three mounting points on the frame should all be on the same plane if the frames not tweaked. The stacked up height of the cross sill, cross sill bracket, and wood block should be the same as the rear sill mounting brackets for the bed to sit level. Some vendors are making cross sills taller than others and some have different height blocks. Just make sure you check the height of blocks-cross sill-bracket combination and it should be 4", same as the rear sill mounting bracket. Adjust the wood blocks accordingly. If you use the rubber pads, they should be placed at all bed mounting points.
Yes I did this as per your recommendation and it all came out fine. I used the Jim Carter blocks and insulators and ended up running the blocks through the table saw, cut them down from 2-5/16 to 2" even the fit correctly. People buy these kits thinking they should fit, when your straight edge (notice I didn't say leveling , because it isn't really other than side to side) is a great idea.
By the way, the wood blocks with the offset hole go under the cross sill nearest the rear sill. The bolt hole in the frame at that cross sill position is not in the center of the frame mounting flange but is closer to the outboard side. With the offset hole in the block the block sits directly over the frame rail. You can use a block there with the hole in the center, it just makes the block hang over the outer edge of the frame. Not a big problem functionally. Also, notice that on an original cross sill the bracket attached to the bottom of that cross sill has its hole offset as well.