With upsizing to a 318 comes more torque, that will allow you to run less rear gear with any old TF trans, but specifically the A999 will get you a low cruize rpm with reasonable take-off power.
Lemmee run this by you;
>Your wagon probably has 3.23s in the back and the A904 has a 2.45 low gear, giving you a starter gear of 7.91. with 27" tires this will cruise at about 2720 rpm.
With a .72 overdrive this might come down to 1960. A LU TC would knock it down to 1880. Your factory ignition system would NOT be able to supply the correct amount of advance for this rpm, so your fuel economy would suffer. And your throttle would be close to WOT to supply the needed power under those parameters.
>Lets see what a 318/A999 with 2.76s does.
Your starter gear would be 7.56= 2.76 x 2.74, but your 318 would be making way more torque, so the 318 will blast off quicker. In LU this combo will cruise at 65=2230, a much easier target to find adequate cruise timing for. The throttles will end up in a good place and 2230 is a pleasant cruise rpm.
NO overdrive required.
>This swap is so simple, that, if you had all the appropriate parts, tools, and knew your way around a tool box, you could do it in a weekend.
This is actually my dream bodystyle, but I would put a 360 into it lol. I had one in 75, and I have been kicking myself for decades, for giving it away.
EDIT:
OOps I see we are long past this,lol.