[Mr70]

Reflecting the third week of January 1970 at the Leeds assembly plant,this Chevelle could be anything,except an L-78.
That partial buildsheet he's showing falls in line with the time period for this Chevelle,but could be for a number of similar equipped Chevelles,including an Elcamino LS-6.
Quite honestly I would've asked everything you are asking 7 days before you pushed the submit button..
If you want to conduct a buildsheet autopsy now on this Leeds assembly,try looking behind the entire backseat support cushion bunting,then the backseat bottom bun.Look at EACH hogring to spring connection,as you will most likely find something scrooled up there.Then remove the rear package tray cardboard and look between the jute.Look behind the two side ear muffs at this time too.Then remove the rear 1/4 panel trim and check behind each.If still nothing,remove each interior door panel & look behind there.Look inside each metal door & 1/4 panel pocket,as sometimes the buildsheet releases from the cardboard structure and falls in here.Remove the back of each bucketseat back as well as the bottom springs & inside the cushion covers too.If still nothing try removing the carpet and look everywhere,specifically at the metal floor around the rear center hump portion,as well as the underside of the carpet.Don't be afraid to peel up the sound deadner too.
Look behind the plastic floor firewall pedal gaurd also.
Look ontop of the radio & behind the back of the glovebox as they sometimes taped them there in extreme situations.
If still nothing remove the two metal pillar support covers and look behind them as well as INSIDE the pillars.It could be scrolled up there and difficult to detect.If still coming up empty,try releasing the roof headliner and look up in there.
The other non interior areas you can check are inside the upper rear 1/4 panel areas that are inside the trunk.Remove the Door Jamb vents near the striker,and shine a flashlight way up in there too.Don't be afraid to reach your hand in there and brush the very lower floor area.
Try inside the front fenders,between the inner wheelhouse and the fender.Aim for the battery tray and voltage regulator areas behind the headlights too.
You can drop the gas tank too,but this area wasn't favored heavily by Leeds,my experience has shown.
I wish you success with this vehicle.