In performing a holistic crossover from Weber carbs to oem fuel injection, I have snagged on a couple items; bad fuel lines and a broken throttle control pedal.
The throttle pedal on a 914 is a rubber covered steel structure with an embedded hinge. The hinge is enclosed in rubber and tends to rust out, making an imprecise throttle control. A new throttle pedal is about $35. Not only was the pedal hinge gone, but the bolts securing it to the floorpan were frozen, ripping a hole in the pan when attempting removal.
Remove pedal box assembly.
With an air angle die grinder, and a 1mm cutting wheel, cut a 3 inch by 12 inch segment from the pan under where the pedal box assembly mounts. Orient the cut to encompass the rigidity structure under the floor pan, stopping the cut just below the master cylinder mounting studs. (in this case, no need to totally remove the stiffener underneath)
Inspection of this structure shows massive rust and thinning to the point of ruin. This segment must be reconstructed. The technique is variable, ranging from the purchase of a salvage yard torched part, or fabrication of a new structure.
I choose fabrication, from flat stock. Measure the rectangular hole you just cut, and begin by laying out a flat piece for the floorpan, sized to fit as appropriate for MIGing in place with 1/16" gap all around to allow weld penetration and expansion.
Fabricate the stiffener from drawings made from original.
Cut and size a single piece for bending on a brake, or construct from flat stock. I choose flat stock because bending this channel would require a Di-Acro, I reserve use of that for only the worst situations. (I would have to ask someone to do this for me).
Using flat stock of needed shape and size, brake bend the 'halves' of the channel, then weld the channel into one structure. Not as pretty as a single, bent piece, but just as strong for this application.
It is now time to replicate the mountings for the pedal and pedal box.
The throttle pedal is fastened with two M6 X 16 bolts, and the pedal box is held with two M8 X 12 bolts at the floor, and two bolts at the front bulkhead, shared by the brake master cylinder.
Carefully index these fasteners using the original part as pattern.
With two M6 nuts, spot mig weld these after drilling pilot holes.
Check the fit constantly as you work because welding can warp dimensions. Weld all nuts and fasteners into the structure, and combine the two segments into one solid piece.
With all holes, studs, and nuts in place it is now time to prepare the floorpan site for fitment and welding.
Thoroughly clean the site of rust and bituminous/pvc coatings, then offer up the patch to see how the edges line up and how much gap exists around the periphery.
Adjust the patch (or hole) to fit, then begin tack welding, first at corners then alternating side to side in similar fashion to torque sequencing head bolts. Tack weld all around until the tacks are one inch apart, then weld fill in the entire periphery.
Check penetration of welds to insure fusion, then grind weld beads smooth, but not flush to panel. Inspect again for voids, filling them in. Coat the bare metal with 'cold galv' spray inside and out, then apply bituminous sheet to affected area of interior.
On underside of body, restore coating integrity with spray undercoat of rubberized variety. Let dry and reattach hardware.
Pelican Technical Article:
914 Restoration of Pedal Box Floor Area
Porsche 914 (1970-76)