single diode mixers are VERY common in 2GHz and up, they are VERY efficient up there, you just need care to choose the right diode.
It's a long way from 50 to 2000 MHz! You don't see many lumped-circuits at 2 GHz, and you see even fewer stripline circuits at 50 MHz. Diode mixers are popular at millimeter wavelengths because, with sufficient LO drive, they can give wider dynamic range, and they're cheaper. But they need a low-noise active stage ahead of them. If I were going to use a diode mixer, it would be balanced, not single-ended. If you have to develop a large LO signal you might as well get the benefits of balancing.
Active devices have no net loss like diodes, and for VHF and lower frequencies they are cheap and easily obtained. The gain of an active mixer will offset losses in filters, and require much less LO drive. At 50 MHz a J310 used as a mixer has a noise figure low enough that he may not need an rf amp; with a diode mixer he almost certainly would. Remember, this converter is going in front of a regen IF, and will be used with a simple antenna; it only needs a low noise figure, not dynamic range.