I think I can help you/him out.
Yes, just about all the Mustang parts are interchangable. The best advice to give him is this web address,
www.tccoa.com .
My advice would be to start out like any other car, open up the intake and exhaust. The stock exhaust on the 96-97 Tbird is the most restrictive thing you've ever seen. A single 2 1/4" pipe that is pinched down to half of its diameter. There are a number of different options he has for exhausts, so tell him to email me or check out the website.
Next he should get a 80mm or 90mm MAF from a SVT Lightning and get an Inject Tech chip burned w/ the MAF tranfer function. This is the best chip there is.
3:73's are a great choice, all though they will be a little more expensive to install then on a normal mustang because the Tbird has IRS, but no biggie.
Skip the bigger TB, because the gain will be so very small, and that money can better be spent somewhere else.
And the pulleys, of course they are always a nice help.
My email is jackthemack@snip.net and I can go into more detail for you. But you have to go to
www.tccoa.com and post this question on the Tech BBS and you will get all the help you will ever need. I'll look for your post over there.
Ohh, BTW, just w/ the chip, MAF, and catback I went 15.2 @ 91, so w/ the rest of the exhaust done, pulleys, and 3:73's, he can go deep into the 14's.
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1997 Thunderbird 4.6L: Dynomax exhaust, Lightning 80mm MAF with 7" powerstack cone filter, B&M 24,000GVW trans cooler, Inject-Tech chip, KVR Brake upgrade. 15.2 @ 91. Not bad for a 3800lb auto 4.6L
No Longer own: 91 LX 5.0L 5 spd