i have fitted inertia belts from the club to my 13/60 saloon and wished i had gone for the static type as the inertia belts retract behind the seats and are difficult to pull back over my shoulder without opening the door,also they seem uncomfortably tight.
removing the securing bolts from the mounting point can be a real b-tch of a job as they tend to sieze and have to be wound out to the last thread---if you can get some wd 40 or something on to the bolts from under the sill it might help,it took me a couple of hours just to get the bolts out.
good luck