When it comes to rear axles, GM offered a ten bolt 8.5 inch carrier and for heavy duty performance mills, a 12-bolt Chevrolet made carrier was supplied. Both were more than adequate for stock performance at the time.
In every model year, the Super Sport trim is highly favored among muscle car fans. The Malibu trim is also a strong contender especially in V8 form. Certain packages were made only a few years and are getting a lot of attention nowadays. This includes the "Heavy Chevy" package in 1972 which was an insurance beater Chevelle minus the SS emblems. These are getting serious attention since by 1972, the SS package included the 350 V8 engine for the first time, diluting the raw power image of the SS. Heavy Chevy is very similar to the SS yet sells for less and is rarer. Any convertible Chevelle is a desirable car and certain ones are scarce such as 1969 and 1972 SS models.
It should be mentioned that the entry level 300 Deluxe cars are popular among retro drag racing fans for their light weight and favorable class ratings in NHRA events. It was possible to get a 396 engine built for a limited time, the 1969 model is a notable example of this. If the 300 series in question is just an inline six car, the price will be cheap. It's the factory V8 powered ones that are commanding higher prices. The 300 series are notable for their post body construction and taxi cab economy interiors. They are the only 1969 Chevelles made with vent panes other than the station wagons. The two door station wagons are popular with fans who haul a lot of gear. Even the four door wagons are getting attention. So many have been gutted for parts over the last 20 years that finding one nicely equipped in restorable shape is difficult. The days of parting one out for their 12-bolt axle, heavy duty transmission and V8 engine are gone unless it has terminal rust.
When it comes to desirable options, the obvious ones include air conditioning, power disc brakes, variable ratio power steering, custom interior with bucket seats and full rally gauge instrumentation. The top performance engine was the L78 375 hp 396 which was available in limited quantities until the end of 1970. The top 454 engine was the LS-6 450 hp, which was available for 1970 only. From 1971 onwards, only LS-5 was available and is the most desirable big block. The Muncie M22 Rock Crusher transmission is the most desirable performance 4 speed. The TH400 is usually paired to high performance engines like the 454 or 1968 396. Otherwise a TH350 or Powerglide was used. In order of preference, automatic transmission choices are TH400, TH350, then Powerglide. Rare options included K66 transistorized ignition, L89 aluminum heads, rear window defroster, AM/FM stereo, 8 track player, cowl induction hood, heavy duty boxed frame (for non convertible cars), limited slip differential.
The hottest 396 was the solid cam L78 available from 1968-1970.
Chevelles have been hot rodding favorites ever since they were new. It's safe to assume half the V8 Malibu cars you'll encounter will be modified. The SS models have been heavily saturated by media coverage as valuable icons of Detroit's muscle car era. Plenty of those models have been restored the last twenty years. There are a few things to look out for when eying a potential buy. From the 1968 to 1972 era, Chevelles used open channel frames with swaged side rails for extra rigidity. These cars were a bit too flexible when a big bore manual transmission V8 was installed. Frame twisting is common with drag raced examples especially if unreinforced. Check the rear control arm to frame mounts and control arm to rear axle mounts for worn out or stretched bushings, broken collars, out of round eyelets. They're signs the car led a hard life and will need work, if not chassis alignment.
The front frame horns will display accident damage repairs from front end collisions. It's possible to line up sheet metal to fit properly and still have bent frame horns. Look at the first few feet near the steering box and front sway bar mounting areas. Check it with a magnet if you suspect putty was used to smooth out a repaired frame. Check the inner side rails for rust out or crumbling metal. These rails hold moisture easily. If the frame looks good, turn your attention to the body mounts next to the toe boards on the lower firewall. Rust often forms there due to water retention. The boxed structure for the frame mounts may be rusty and cause flexing under acceleration. Really poor examples are missing the rubber frame separators leaving the frame to chassis bolts unprotected. These faults are repairable, but should be considered when negotiating a price.
Floor pans can rust but the model isn't known for weaknesses in that area. The entire trunk floor is a rot spot however, due to water leaks from poor sealing rear windows. Check the underside of the trunk lid hinge area for rust and water stains. If the car has a vinyl top option, you are almost guaranteed rust formation under the vinyl between the rear window and the trunk. The filler panel is notorious for disappearing. Replacement panels are available but the labor involved is going to cost if you can't repair it yourself. The trunk floor is commonly rusted out. The worst spots are the inner rear wheel wells and lower quarter panels.
The rear window filler panel to trunk floor area is rust prone especially on a vinyl roof car.