$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)
2003 Explorer WAP block with Modular Head Shop "street ported" heads and Stage 2 PI NA cams, 75mm Accufab throttle body, C&L upper intake plenum, Kooks 1.75" primary/3" collector headers, 2.5" full exhaust with mid mount Magnaflow dual in/out muffler, 24lb/hr injectors, 80mm MAF, Tuning from Don @ www.lasotaracing.com
, 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 with 35mm offset, 255/40/ZR18 Tires, Front and Rear strut/shock bracing, GR-2 shocks, Eibach 1.5" springs, 1989 SC front and rear sway bars.