Whether you car is stock (tolerance stack up being a fact of manufacturing life) or modified it will pay you to check your drive shaft for proper fit.
Put the car on a drive on rack or on jack stands.
With the cars weight on the suspension as you would drive it, disconnect the shaft from the pinion yoke.
Push the drive shaft forward till it bottoms into the transmission.
You should be able to drop the rear u-joint cleanly past the pinion yoke without resorting to a tool of any kind.
Any clearance up
to 3/8 inch is fine.
More than 3/8 inch clearance and you are running short by the excess. The greater the excess clearance, the sooner you will be headed for the transmission shop.
The cure for this is very simple. You can have your drive shaft re-tubed to the proper length or you can buy a complete replacement shaft. Both Inland Empire Drive Line and Summit Racing Equipment sell replacement stock length shafts and shafts made to compliment various manufacturer's trailing arm kits.