120y eith l series is pretty straight forward, either mod the existing x member for the l series mounts or use a 180 x member but it mucks up your steering gemometry a bit (ask rev head).

You will need a auto tail shft for the conversion so buy an auto 120y if you can, and use the 1600 5 speeds or 4 speeds (stumpy) and should bolt in easily enough for you.

Tunnel is ok in 120y for the L series as same for auto or manual.