You can actually get the supa 5 brakes to work well. SAFTEC will reline the shoes with decent material and machine to size. Alternatively, get oversize lining fitted and get them machined locally. Put a 20thou shim each side of the cam and the fit will be perfect.
Much of the problem with the brakes is down to excess clearance between shoes and drum. The brake cam is shaped to give maximum mechanical advantage with minimum clearance between linings and drum. After that the shoes operate on a larger radius and leverage is lost. If you look on Real Classic website I did an article years ago, with photos. I think it’s easier that fitting a TLS brake.
TLS brakes are ok going forward but don’t hold you very well in reverse, as on a hill.
Also, make sure the brake cable is strong, with no spring in the outer.
Cost about £30 inc p&p.
Hope that helps.