$300 for an explorer motor is a no-brainer. Yes, swap your Mustang PI intake in place of the explorer one. As far as your injectors go, yellow is 19#/hr, orange are 21#, light blue are 24#, red are 30#, dark blue wide body ones are 36#, dark blue skinny body ones are 39#, and green are 42#.
For the timing cover, I'm not 100% sure, but I think you could keep the explorer timing cover as long as you also keep the explorer water pump, belt tensioner, and belt routing.
I don't see any real issue with the explorer belt routing, it's just different than the Thunderbird. I think they have the AC compressor up top, but as long as it fits under the hood, shouldn't be a big deal right?
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.