Jnfbodyguy83:
You will need a big block A727 transmission (you probably have an A904/A998/A999 right now with the 318), you will need mounts for that, and most likely a shorter drive shaft. Shumacher (and others, maybe) have the transmission mounts for the A727. You may nor may not want a new rear end, the 8 1/4" rear can take a the torque of stock, non-high performance 383/400, but anything more than that, and you may need to look at an 8 3/4" or stronger rear end. I don't know if you want headers or not, but Schumacher and TTI make so called "block hugger" headers that will probably be required for clearance reasons. I don't know if it will be required, but don't be surprised to learn that a cooling upgrade will be needed as well. With the added weight (which really isn't all that much, 100-150 lbs. or so), a braking upgrade is a good idea, and you may want to consider stiffer torsion bars.
I am considering a long term swap like this, and have looked into it some. I am hoping to get my Mirada street legal and use it for a while before making a final decision regarding an engine swap.
Kostas