I have already replaced the saw filter in two of the SDRx boards to operate on the GPS L1 frequency. This works very well. I used a hot air gun to reflow the SAW in place of the original one (the footprint is quite standard).
Bypassing the filter does not work, the R820 tuner is saturated with unwanted out of band signals (GSM1800 mostly). It is the same as when you connect an LNA to a normal rtl-sdr stick without any filter in between.
I was just wondering if the LNA (without the filter) is broadband, or if the chip is already intended as an L-band LNA (eg, a GNSS frontend). With a UHF SAW filter, would the receiver work well on a UHF frequency in its passband without changing any other components?
SAW filters for the 70cm ham band should be available. At least for the ISM portion of it I have held them in my hand. I did a quick search at Tai-Saw and found this one: TA0693A. It covers the 430-440MHz 70cm band You can find some stores on the internet selling it (4-6$), but getting a sample should also be possible. The footprint is not the same as the SAW currently installed in the SDRx (frequency is lower so device is bigger), but it will fit on the footprint to the left of it:
VHF saw filters for the HAM band I have never seen. They will be quite large also. This is a primary exclusive allocation for HAM so there is likely little commercial interest. You can have a custom SAW made for a competitive price if you buy a large enough amount (eg, group order, …)