The blocks are just Alder I believe and I would have to measure but 2x2x2? You could simply cut your own to the desired height. It would be tall and may be a bit wobbly. If you are building a street machine why not build them out of square tubing? Put rubber pads in and that may solve your issue. I have never used the covers, they are sold as described. In two spots at the fender bolts they are secured, you could add small bolts at the ends to kill the gap.