Replacing, and/or re-indexing the torsion bars is one of the harder jobs on the 944...physically and mentally.
Physically... you have to remove the ENTIRE rear suspension and running gear. (two or three times if you don't get the mental part right.)
Mentally...you have to calculate and calibrate changes in torsion bar spring rates, ride height, un-sprung position, and weighted positions.
But, you already knew that.
We installed new 30mm torsion bars two winters ago. Took us 4-6 hours to remove all the suspension. Another 2-4 hours inspecting, marking and re-thinking the proceedure. Installation was another 4-6 hours. We did it over two weekends.
Shops will probably want a minimum of 12-14 hours for labor...maybe more.
Good Luck
JM