The front spacers are no more than 1/4" thick rubber. The rear is a little bit tricky, those "L" shaped blocks are made of plastic, but you could fabricate something out of 1/8" plate, 6" x 6" maybe. You'd need to bend it to look like this:
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You'll be able to get the right height measurement once you get it on there, but I think it's around 3". You could even change it a bit if you like to use a bolt.