You need a 1.1 or 1.2 8v SPI engine (punto 55, 60 or Cinq Sporting or early Sei Sporting), Cinq or Sei Sporting gearbox, driveshafts, clutch and gearbox cables, reversing light connector, and -- I think -- engine and gearbox mounts. Plus all the main hoses.
Might as well grab the shocks and springs off the Sporting while you're at it.
If the 899 is a Sei, I'd just find another. If a Cinq, it's probably worth the effort.