I just paid too much for a B&O MMC20CL off eBay. I hope I will be happy.I think that I was looking at that one too . . . glad you got it. If it's in good shape, then you didn't overpay. Stellar cartridge.
On the AD797 - this opamp is capable of extremely high performance, but it's definately NOT one to swap into an existing circuit without careful consideration, especially if it originally uses TL072s! The AD797 really shines with low source impedances (not MM cartridges), but on the other hand, it can be limited in its useable output current . . . so it doesn't necessarily do the best job of driving the low-impedance feedback network that suits its low eN characteristics. That's why I used the discrete JFETs as a buffer, and why I used it in the second stage, where it can be driven from the low source impedance of the first. The AD745 is FET-input, so it works great with an MM cartridge . . . but it's not stable at lower gains, so stability and phase margin have to be carefully considered in application. Then there's the fact that the TL072 is a dual, and AD797 and AD745 are singles.
For general TL072 replacement, try OP249.