Alan,
 
Floscan senders are used by GRT amoungst others - there must be loads of GRT EIS & EFIS installed, so I wouldn't imagine finding somewhere to put the sender would be too tricky. The mod process looks daunting, but isn't. Its design to frighten off the tinkerer. Most of the evidence will be in service experience from other aircraft with the same installation - you only care about the sender not restricting the fuel flow or getting blocked as the LAA aren't really concerned if the unit is accurate - that's your problem! The always want to approve any fuel system mod so you probably won't be able to use someone else's submission, but you could ask. You might also be able to justify it on safety grounds as potentially more accurate than gauges?
 
Pete