Bottom of cooling jacket: Not super thick

I guess I understand your perspective. But I'd rather follow what the smarter folks that made the equipment say to do - which is use the correct coupling gel. I'm not going to pretend I know better (not saying you are pretending - just a turn of phrase).
I'll add - just clearance the block. Give yourself .100" clearance and move on. Ive done probably 20 over the years. Some making 1.7hp/inch with the nitrous. The bottoms of the cylinders are not what one worries about.