A '66 will have disks front, drums rear, single circuit brakes.

Stock tyre size is 165-15

Most likely is floor shift for manual transmission.

If you live in a rust area, front wing mountings, they are a box section and rust, visible in engine compartment if really rough. Front wings themselves, available but not cheap.

Cross member under radiator.

Front outriggers under drivers/ passenger floor

Rear wheel arches, all models

Lower front screen corners, and metal extending down from there

Lower section of rear wing over sill if it is a 2 door model

Seams between inner arches and bootfloor

After that it is all the usual stuff door bottoms, bootlids, tailgates and floor pan.

If you are looking at a Wagon/Estate/Combie depending on nationality check the seam between the gutter and the roof very carefully it is nigh on impossible to fix permanently when they start to rust there.

No real mechanical weakspots, noisy timing gears, camshafts. Excessive play on the rear axle pinion. Personally I would accept any mechanical fault if the shell is good and the price is right. Overdrive is nice, but retro fittable

The other thing I would check for carefully is accident damage, especially saloons soriously don't like being rear ended, creased rear arches are a dead giveaway. You will tend to find that price differences between real dogs and superficially scruffy but fundamentally nice cars is not that great, It is really worthwhile seeking out a good'un,whatever your budget.

Regards