Of the systems that maintain the stock shock towers these are my thoughts. The RRS setup is very nice but pricey. The trick to to keeping the stock steering geometry is to maintain the dimensions for the inner tie rod mount points. This requires a center hung R&P of which the GM unit that Steve and I have are the most common. The downside is that the center mount adapter has a lot of flex unless it also get's supported on one end with a sliding bearing. There are two companies that do this. RRS and Total Control. Unisteer doesn't have this but seems to have been heavily beefed up to compensate.

Then there is the Mustang II solution. There are two that are popular for Falcons. One is Heights and the other is R&C Motorsports. I can't offer much about the details of these. They open up the engine bay so you can get any engine to fit. Even the new Coyote 5.0 is an option.