The difference between your DOHC and the Mark's is the tuning and exhaust. The Conti has a quasi-dual vs. the LSC's true dual exhaust. They have the same engine, except the Conti is FWD and the block is cast to fit that way. The internals, heads, and intake are the exact same thing.
Lincoln de-tunes the hell out of the Conti because of the transaxle. Your car has the ultr-crappy AX4N transaxle, which is the exact POS used in the Taurus/ Sable. The Mark has the 4R70W, which can be easily modified to handle some serious power. However, the Taurus/Sable puts out a whopping 140 hp with that transaxle- vs. your 275 hp, which is pushing it. Those tansaxles break down pretty easily if you beat on them, so be warned.
If you want to beef-up the prefromence, the first thing I'd go for is a shift kit from B&M, they're the only company off the top of my head that has a kit for the AX4N tansaxle (for around $125 IIRC). Combined with a chip, you can shorten your shifts and reduce friction, correct up/downshift irregularities, and extend the life of the transaxle. A chip will also correct the shifting, engine timing, raise the rev limiter, and speed limiter.
Next, port n' polish the heads and intake manifold. The intake manifold you have is identical to the Gen-1 Mark VIII intake manifold. If you have it worked, you can get more power. The heads are also identical (B heads)- and work even better with some port/polishing work done.
A less-restrictive, free-flowing exhaust will also be of benefit. Upgrading to true dual will be a bitch since the Conti is FWD and the transaxle and other parts get in the way; but there are plenty of that are options availible.
For real power, a 50-75 shot of nitrous will get your car going. Anyting over that will require fuel system upgrades.
With a chip, shift kit, P&P work on the heads/ intake, you should achieve your goal of 300hp, and be running low-mid 14's. Nitrous will bring you into high 13's, but the transaxle may not be able to handle the power above a 50 shot without some serious upgrades. Since the SHO Taurus sits on the same platform, you may be able to use the high perfromance Mazda transaxle from a SHO Taurus. That trans can handle over 350 hp easliy, as many SHO folks have superchargers and NOS that puts them over 375 hp; but again, that's if you want serious power.
Good Luck!
