That pickup is most likely a 1969 or 1970.
The 1971 and 1972 models had a higher nose on the hood above the grille.
My first brand new car was a 1972 Chevy Suburban C20 with the 402 cubic inch big block. This was a 396 type big block with a few more cubic inches. The GVW was about 7200 # or so and the light weight was about 4250 #.
It came with a 16 gallon fuel tank. I had an aftermarket shop build a 50 gallon fuel tank for me in the 1973 oil embargo.
There were only 2136 C20 Suburbans made with the swing doors like mine in 1972. Versus 95,000 C20 long bed pickups.
People today don't remotely have the ingenuity of the past truck camper manufacturers. A 3/4 ton or one ton SRW pickup would carry the very heavy TC's of the past for thousands of mile trips every year on the old style tires of the era and very seldom did you hear of any blowouts or truck frame failures. TC's were very popular in the 1970s and 1980s and most were carried on 1/2 tons or 3/4 tons. Dually pickups were few and far between then and they were basically spartan work styled trucks.
We bought our first TC in 1965 (a Georgie Boy decked out and with a bathroom made in Red Bay Alabama for $1270 out the door new) and carried it on a 1966 Chevy 3/4 ton with a 292 six cylinder pickup with a 5 speed floor shift and it had a creeper gear that worked great for pulling our 28' Owens wood plank very heavy cabin cruiser out of the water at the ramp in the fall and putting it back in in the spring each year. Stored the boat on our other side driveway and decorated it for Christmas and had a big translucent Santa on top of the flying bridge with a 100 watt light bulb inside. Made the front page of the newspaper!
Drove the '66 truck for camping etc use till it had over 140,000 miles on it all over the USA and Canada and never had any tire failures, frame issues, or drivetrain problems. Most miles were pulling a 17' or 19' fiberglass outboard boat or our motorized 250 CC dirt bikes etc on a trailer behind the TC/truck combo for many years. Finally bought a new fancy 3/4 ton V-8 truck with an auto tranny and 4 wheel drive and have never looked back. Kept our two larger boats in a marina and stored them there as they were too big/heavy to pull out in a ramp and over 12' wide so a hoist was required. Then on to our first diesel.
These were our personal trucks not the ones we had for our business.
A superb CC LB 4X4, GM HD Diesel, airbags, Rancho's, lots more
Lance Legend TC 11' 4", loaded including 3400 PP generator and my deluxe 2' X 7' rear porch
29 ft Carriage Carri-lite 5'er - a specially built gem
A like new '07 Sunline Solaris 26' TT