I realize that I've got three questions running at once on this forum. One on FI, one on head swap and now this...but they are pretty distinct topics and searches didn't quite answer all of my questions. Personally, it looks like I'm going to have to save up for a while longer to do the heads right (or just buy a new BP Engines crate motor )...so I'm looking for a stopgap measure to still be able to have some fun this summer. Perhaps a cam/valve spring upgrade could do the trick for now. Based on the Magnum 380 crate engine, it seems like there's at least 80hp to be had from a cam/valve spring/intake upgrade over a stock 5.9L which is pretty amazing. Unless I'm mistaken the difference between the Magnum 300 (which I have) or a junk yard 5.9 are relatively minimal. My question is about whether or not this is the best we can do on the stock heads/rotating assembly or if people have done better with a custom grind? If you've gone this route, how did your motor come out? Is it possible to get some good lope/overlap sounds? Would the use of a dual plane intake be a detriment? I have to figure that Mopar Performance went with the single plane for a reason... So the question was asked in general so that it might benefit other forum members....but before anyone asks, here's my application: '73 Sport, nearly full weight (fiberglass hood and a few weight reductions here and there. The drivetrain consists of a somewhat built 904 (TF2 shift kit, ~5800 rpm governor weight, stronger bands/clutches, deep pan), a TCI Streetfighter 2600 rpm stall, aluminum driveshaft, Moser 8.75" with Eaton helical limited slip, 4.10 final drive. Almost all of my work so far ha s been suspension/steering/brakes, all focused around handling. I prefer to use my car for general backroad hooligan driving so I really want a motor that breathes and feels relatively happy revving out upper 5ks at least. Can that be accomplished with stock heads? Is it worth the trouble? Once again, any experiences or opinions are extremely welcome.