The 1991 and newer Lincoln Town Cars used the 4.6L SOHC V8 which is 281cid not 289cid.
It will fit in a Mustang with some work, Hot Rod magazine along with a few others have detailed modular (4.6/5.4) engine swaps into fox-body Mustangs.
Among the things you'll need would be a 1996-2004 Mustang GT K-member (for oil pan clearance) matching motor mounts to the K-member, matching
tranny mount, and an exhaust system (1996-2004 Mustang H-pipe would probably fit with few modifications).
This wouldn't be a drop-in and plug-and-play swap, there'd be wiring involved (you'd have to modify the Lincoln's wiring harness and install it or upgrade to a 1996-2004 Mustang harness and electronics and install them, neither is plug-and-play for a fox-body because a lot more functions are electronic in the Lincolns and newer Mustangs).
If it's something you want to do, then by all means go for it. But your better bet would be to sell the Lincoln and/or it's drivetrain, and use the cash to buy a 5.0 out of a fox-body Mustang and swap that in. That's a much easier swap (not that it doesn't have its own share of complications) and would be more powerful and lighter. An even easier alternative would be to sell both cars and use that cash towards a 1996-1998 Mustang GT (these cars are among the cheapest performance Mustangs out there and the parts are there to turn them into Corvette-beating monsters.
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1976 Ford Mustang II Ghia: 302 with a 600cfm Edelbrock carb, Edelbrock Performer 289 intake, Dynomax Blackjack headers, 2.5" exhaust with Flowmaster Super 44s. RJS 11-gallon fuel cell, C4
tranny, chrome 16" pony wheels, fuzzy dice, brown vinyl half-top, and painted in the tackiest color ever (harvest gold, that's why I call it "The Goldenrod").
Also have a 2003 Dodge Ram (lightly modded daily driver/tow rig/office/dining room/home away from home/workshop... I call it "The Big Blue Dawg".)
1993 Mustang 2.3 motor swap 
