Without even looking at the schematic (actually having no idea What a Hampton preamp is) , I can tell you that E80CC and ECC88 are very different valves, only the pinout is the same. How did you get the idea that they are interchangeable? Maybe you meant E88CC? This would be compatible, ie same valve, different specs (long-life, microphony, noise etc). If you plan to swap E88CC for ECC88, you are not going to do any harm. The sonics will likely change a little (possibly for the better), but this is subjective. Try and see what you like best.
Point blank, tubes are simply not quiet enough to drive directly with a LOMC cartridge. Either you use a hybrid cascode, ala Allen Wright, or you use a step up transformer (SUT) at the I/P of a "conventional" tubed phono circuit.
At the μV. signal level LOMCs produce, S/N considerations are paramount. IMO, the only tube with a snowball's chance in Hell of doing the job adequately well is the 6C45П (6s45p). The type is difficult to work with, as it will oscillate if you glance at it too hard. Why struggle to obtain a marginal result? SUTs and hybrid cascodes have a "track record" of doing the job well.