Nothing wrong with those numbers for a basically stock 440. In fact, that is just about exactly the kind of numbers to be expected.

My old 470 motor would make about 475 RWHP and it was a tad too radical for a daily driver. I agree with your dyno operator, if you start making too much power it gets to be a hassle. Parts do start breaking and the maintenance does go way up.

One option is to go with a stroker motor but to keep the cam, intake and carb on the conservative side. That combination gives you lots of torque at a lower rpm which gives you good pulling power. By not having to turn the engine really high you avoid a lot of maintenance and part breakage. Of course, it costs a bunch of money to add displacement.

It all boils down to choices and money.