I'll check out the Gerson mask. Thanks for the tip on sealing the filters, makes sense.
Could you clarify something I came across in the 911 Workshop Manual on using the P836 Front End Gauge? It states, "Measurement and take-up points are welded in the floor plate since the 1975 models. This facilitates the damage diagnosis considerably." I think they're referring to the lateral Dimension 1200mm C on the Floor/Frame Assembly diagram below:
On my 73 tub there are 2 punched holes in roughly these locations. Do these holes coincide with the points welded to a 75 & later car? Can they also be used for dimension checks?
Thanks again for your help,
Charles