You would need a voltage stabilizer, and a tr4 sending unit. I'm not sure offhand, but ISTR the 4A gauges each had their own bulb for illumination, so you would probably want to wire that into the existing dash lights.
Otherwise, I think it would work. Might need to tweak the calibration a bit for different fuel tanks, but it would probably ly be OK as-is.
Early TR4 fuel gauge looked different than the later ones (curved glass vs flat plus the shroud over the needle pivot). Seems like maybe there was a further cosmetic change for the 4A, but not certain offhand.