Having had a stock and modified LD-340, I can say that heavily modified intake (MP instructions and further porting) made excellent power up to 6800 when so properly equipped head & camshaft wise.
The stock LD-340 was and still is an excellent street intake—- for the right price. If overpriced…. I’ll pick up a used RPM/AG and not ever think of an overpriced LD-340. IMO, the stock LD-340 can go 6K easy.