Sorrry I should know this from your previous posts but what sidecar combo do you have?
Anyhow.....You can usually get lead wheel weights at a garage or tire shop cheap. Melt them down and pour the lead into a steel tube or something that you can bolt on somwhere. Note that melting lead can be dangerous. Be sure there is no water or moisture anywhere ...anywhere. Make sure tube or whatever you are pouring it into is dry etd etd,.,,no moisture none.
You can cast a bent bolt or two into whatever you are using for a mold for attachment purposes . Old car valve covers work good. No moisture or oil...dry dry dry.