detonation / knock issue on 340

What carb is it? If it’s a Holley call BLP or maybe ProForm is still making parts and get a billet plate.

That reminds me BLP offer slabbed throttle shafts for increased air flow: 4150 Pri Shaft Thinned/ Coated Thinned shaft [102264-BX1] - $42.99 : BLP, Xtreme Performance Made In USA