I have an 07 Monte ss with 5.3 for my DD. And a f150 for work. I plan on making her my summer weekend car. Something to work on and only drive in the warmer months. So I'm not too concerned about rust. Just got to keep it clean.
Go with 3.73's and a TL unit then, that will wake it up a lot. PI heads/cams/intake and fuel rails off a 96-97 will get you more power as well.
97 Thunderbird LX (The GT Bird)
PI Swapped NPI motor with some port work on the heads, PI cams, 80mm MAF, CAI that feeds from fenderwell. Jmod, 3.73:1 TL in Mark VIII carrier, Mark VIII aluminum LCAs, 93 Mark VIII driveshaft, PBR brakes (soon to be Cobras), 18x9 wheels, 255/40/ZR18 Tires, Front and Rear strut/shock bracing, GR-2 shocks, Eibach 1.5" springs, 1989 SC front and rear sway bars.