emac:
Age doesn't matter if you're agile.
Do you have the Bentley?
Take your time and lift the rear securely.
The tricky part is the connection of the cable in the pedal cluster up front, tight space and you'll need Fingerspitzengefühl. (Finger tip dexterity) to install the clevis and clevis clip. Extend the new cable a good 1/4" into the clevis and lock the nut and the clip.
I suggest you first inspect the pedal cluster before starting because you may need a few more parts. SC Bentley 301-7 to 9.
Parts that can wear:
#14 Pedal Cross-shaft cable-connect lever,
#16 Bushing,
#5 Clevis,
#2 Roll pin
930-423-027-01-M260 Pedal Shaft, 911 (1977-86)
Brand: OEM [Photo] $39.00
999-166-001-02-M260 Snap Retainer Clip / Pin For Clevis Fork (clutch cable to pedal shaft), 911/912E (1974-86), 911 Turbo (1976-88)
Brand: OEM [More Info] $3.25
900-309-002-00-M105 Clutch Pedal Roll Pin, 6x28mm, 911/911 Turbo (1974-86) Brand: Canyon [Photo] $1.00
You may also find that the bushings in the pedal cluster are worn and need to be replaced.
Go for the brass bushing kit from Pelican:
10-1792-423-M105 Bronze Pedal Bushings Kit, 911 (1974-86), 911 Turbo (1976-88)
Brand: Canyon [More Info] $14.25
Refurbishing the pedal cluster including painting the housing #20 gives long-time peace of mind.
Before installing/adjusting the new cable, make sure the long actuating lever for the clutch on the cross-shaft moves freely! If not, remove the circlip, remove the short and long lever, clean and oil the cross-shaft, re-install the levers and circlip and adjust the clutch.
Do you have the Bentley Repair Manual?