After a whole lot of fiddling and various non-working designs, I've come up with this!
It uses two Mini Circuits ADE-1LH+ mixers, Xpresso 50 and 100 MHz oscillator modules, two MAX2611 LNAs (front end and IF), and spits out 150-155 MHz-ish signals at baseband. The system gain is about -5 dB - it requires a high gain amplifier at baseband to be useful. The MAX2611s aren't particularly high gain and there are many losses in the passive mixers and all of the 3 dB pads. I'll build some sort of amplifier and will then be able to compare its performance to the dual SA602 design.
Key design point: