As for the crown vic driveshaft, a stock civilian crown vic steel driveshaft is the right length for the T45 swap, but the police driveshaft is 1" too short. It will physically work to move the car, but it is not ideal. If you want an aluminum driveshaft, you will have to have one made, or get a MarkVIII shaft shortened. The length you are looking for is 56.5" centerline to centerline.
I cheated with mine, I used the aluminum P71 driveshaft but also swapped on the large diameter P71 pinion/companion flange and used a 3/4" driveshaft spacer made for lift kits to do fill most of the gap(there's also a steeda spacer that will work with the stock size flanges but it's only 3/8"). Really even that isn't totally necessary IMO, I used it without for some time, it's not like these are stick axle cars where suspension travel is moving the yoke in and out.
Next up on the trans list is the 99-04 TR-3650. The advantage of this trans is no more 3-4 shift fork problems, and a synchronized reverse. Installation is exactly the same as the T-45 with the added expense of needing an extended range speedcal to make the speedo read accurately.
There are no 99-00 TR3650s, those two years were T45s and they also need a speed cal. Those are the best years of T45 to find though, there were numerous upgrades including carbon fiber lined blocker rings in that year range.
Also, 01-04 TR3650s have their issues as well, the root of the problems may be the fact that Ford improperly speced the fluid level too high, causing difficult shifts in some gears, especially second, and all sorts of TSBs were done to remedy this until it was mostly sorted with the 03-04 units, but the fluid level problem still wasn't corrected until the 05 versions. So be wary that any trans you find may have had an owner applying excessive force to get into gear and bent forks, ground gears, ect. I spent a lot of time and money fixing my 04 trans due to that. Funnily enough all internals are 100% identical in the 05-10 versions and they've generally been regarded as quite reliable, only change besides linkages was the fluid level spec.