1uzfe or 3uzfe triptronic is best swap for it. A big no for 3sfe or 1gfe in Rx8.
2GR can also be considered.
V8 gives you around 7-9kmpl local.
2gr can pull almost the same or slightly better eco.
Parts of v8 and 2GR are available.
Uz falls in a 13-15lac swap
GR falls in 9-10lac swap