There should be a special metal plate washer that spreads the load, plus do not tighten them to tight and smear a small amount of sealer over the gasket and make sure that the cylinder head is totally oil free. That normally does the job on the plus side they are light comprared to the Ali ones.
Just enlarged the picture is your Holley set up right or your timing as you have black carbon deposits on your choke which is a sign off blowing back which is pretty dangerous and a quick way to catch fire, hope you are carrying fire extinguishers. Check your float bowl levels.
This was taken during set up. I've since times it properly and it's now OK... I'll perse ere with the lightweight covers and take the advice. I may have overtightened...