I have long tube headers and it came out 1975 I’m thinking of putting a TH350 down thereWhat year is the 455/T-400? A 98 would have had a medium length T-400, as stated above; however, The driveshaft would have a long yoke on the front, probably machined smooth part way on the inside to seal on an "O" ring on the output shaft, and a CV joint and a "companion flange" on the rear. None of this will work with a short shaft transmission and 7.5/8.5 G body rear end. Depending on your budget, long tube headers would be ideal. Also, be sure to use an early HEI distributor, with a single 3-wire plug. If your 455 has a points distributor, there is no provision to run one on a late model car, unless you add a ballast resistor. Good Luck! with your project.