What I did on my Nomad is use shorter blocks so that I could double up on them. I went for 2x40.3mm blocks, which gave me a bit over double the moment rating I would have had for a single longer block.
I used 15mm rails rather than 20mm rails though. 20mm rails look appealing and I could have made them fit but someone pointed out to me that you want the thing the rails are attached to to be stronger than the rails. If the rails are stronger than the mounting surface (which I’m a bit concerned is the case for you), rather than the mounting surface flattening the rails (which is what is meant to happen), the rails will bend the mounting surface (and therefore not be flat, which is bad for longevity and accuracy).
How much a problem this is in reality, I have no clue.