You're getting some mis-information.
The 68-72 Wagon and El Camino do not use the same frame. They are the same length, but the El Camino frame is boxed and uses a shorter crossmember (just like the convertible). The wagon frame is not boxed.
The lengths and widths are as follows.
1964
L=198.8"
W=74.6"
doors open W=133.9"
1965
L=201.4"
W=74.6"
doors open W=134.2"
1966
L=199.9"
W=75.0"
doors open W=134.7"
1967
L=199.9"
W=75.0"
doors open W=134.7"
1968
L=207.1"
W=75.7"
1969
L=207.9"
W=76.0
1970
L=206.5"
W=75.4
1971
L=206.8"
W=75.4"
1972 L=206.8"
All 1968-72 measure:
front doors open W=132.3"
rear doors open W=134.2"
As far as rust goes, I could only advise you as to the areas that are prone on the 68-72 models.
The rear gate down low in the middle and along the bottom edge.
All along the base of the rear side windows.
The spare tire well, mainly at the bottom.
And along with all of our Chevelles, they rust in the front fenders near the rear, down low.
Also pay close attention to the areas all around the windshield. Especially at the base.
If you find a car that was used in an area where they salt the roads or has a lot of wet weather, you can find rust on the front and rear floorboards as well as the rear quarter panels wheelwells.
The 68-72 frames are prone to rust out near the lowest steering box bolt.
Be aware that with any 64-72, it can be rusted anywhere. In areas of the country where cars rust heavily, these cars can be like swiss cheese by now.
On 68-72's, I suppose you could convert a 2 seat to a 3 seat, but it would be a fair amount of work and require some welding. I doubt it would be worthwhile, unless you have small kids who like to ride backwards. IMO, the storage compartment is far more usefull.
Don't even think about converting a rear single action gate to a dual action gate. You'd need to replace parts of the rear structure. You can't just bolt on a dual action gate to a single action gate car. No go. Also, be aware that the dual action gate wasn't available in 1968. 1969 is the first year.
Disc brakes were optional on all 1968-72. 1968 is somewhat of a bastard year as the calipers are prone to leaking and problematic. The 1969-up single piston caliper design is better. Odds are you won't find a 68 with disc brakes anyway, as they are somewhat rare. And not all 69-72 came with disc brakes.
I lucked out 20 years ago and found a 69 Concours that was well optioned. PS, PDB, AC and a power DAT.(dual action tailgate). It was originally a 350, 2bbl, TH350 and 10 bolt. It now has a 396, TH400 and 12 bolt. Along with tons of other goodies such as a factory rear sway bar with boxed control arms, large front sway bar, dual exhaust. I've replaced the bench seat with factory bucket seats and future plans are for a console, tilt and power windows. I have the console and the tilt column but as still looking for the power window setup.
Good luck with your search.
Good solid original wagons are getting very hard to find.
