you have hit the nail on the head... 11 1/2 bolt pattern. You state you need a new converter, simply buy one with that bolt pattern.
The bell housing and everything else will work except starter.
Your current configuration is probably running 157 tooth flywheel., you may need to run the starter off the FMX, given fords high use of standard parts you won't have too many problems.
Personally, i'd run the FMX....but anyway.
If in doubt, and your in australia, talk to Geoff Dellow. http://www.dellowautomotive.com.au
He is a wealth of information and knows EXACTLY what he is talking about....i have learn't so much off him!