Try more initial timing. 17* is not nearly enough in my experience. A bumpy cam often requires 25* or so initial and all in as soon as the engine can tolerate it at cruise. By 2,000rpm if possible.

Of course all that depends on other factors, too; gears, weight, trans, converter, etc. But those timing events are good targets to shoot for.

Unfortunately, those low compression engines can be more prone to detonation than higher compression units that have good quench because they don't have quench going for them.

Experiment with that timing and see what happens.