[AZKen]

The clutch disk floats until the pressure plate is bolted to the flywheel. The spline in the clutch must be perfectly concentric to the pilot bushing/bearing I.D. because the tranny shaft has a mating spline and a nose into the pilot. SOoooooooooo.....this is what the tool or a spare tranny shaft will do. If you can rig something that does that, go for it.
You are aligning splines, pilot and tranny bolts all at once. The tool is available most places. Plastic and cheap. Should be Pioneer TAT5301. O'Reilly's has it and probably other auto parts stores. $5 1 1/8 x 10 spline

BTW: Just to make sure I don't mislead you, The fork and throw out bearing can be installed over the trans shaft if the trans is installed onto the bell housing first. Our motors have that trapped bolt problem and it may be necessary to mount trans after bell housing is mounted to motor. That's the way I described the install earlier.