I came across this http://www.nooelec.com/store/sdr/sdr-ad ... it-up.html
while looking for something else unrelated. There is a new version with a 125MHz LO and that is interesting because it starts to put 10m and 6m into the range of the SERIT tuner.
The reason it doesn't go higher is because it has a low pass filter in there. The design is open source and done in Kicad which is good because I can access the schematic and PCB design (noted - way too many stitching vias).
It would not take a huge amount of effort to modify this design to cover 71MHz and perhaps also reject the lower HF region. It uses 0805 parts big enough to work with. They are cheap, $40, intended to allow TV dongles to work on HF (though they can now do this directly so what's the point?). I plan to order one to experiment. Note they also work for TX, so it's maybe a way to get a Pluto on 6m. They don't have a pre-amp built in nor the tight filtering you will need to keep out strong adjacent band signals.
Edit - a quick analysis with the excellent AADE Filter Designer shows only the low pass needs to be adjusted. It has an attenuation of ~20dB at 70MHz. The band pass covers ~140MHz-210MHz already which allows for up-conversion from ~15MHz to 85MHz.
AADEs transform function allows you to easily tweak without building and it came up with a set of updated values for a nice filter shape, but this means changing every part in the filter. Going to that trouble you might as well convert it into a band pass filter for the band you want. However, making C11 = 56p, C12 = 5.1p, C13 = 82p, C14 = 27p, C15 = 68p, C16 = 18p, C17 = 56p, L12 = 130n, L14 = 91n, L16 = 100n should result in a nicely matched filter. The loss will be 2dB at 72MHz and 30 dB at 88MHz.
A hack that is good enough is to change just the series resonators, only 6 parts and 2 can be recycled. C12 = 4.7p, C14 = 27p, C15 = 15p, L12 = 120n (formerly L16), L14 = 91n, L16 = 110n (formerly L14). Not quite as good but still has adequate rejection of the FM broadcast band, about 3dB loss at 72MHz and 30dB loss at 88MHz.
A lot of people have a good selection of capacitors but not inductors. If you don't have a 91n inductor to hand you could instead change all the capacitors, so C11 = 56p, C12 = 5.1p, C13 = 82p, C14 = 22p, C15 = 68p, C16 = 15p, C17 = 56p. This gives a response is similar to the above with about 3dB loss at 72MHz and 30dB loss at 88MHz.
Another hack is simply to bypass it and do your FM band filtering elsewhere, e.g. in the preamp.