1979 was the first year trucks under 1 ton were built with convertors, C&C 1 ton trucks/vans were available w/o convertors until, I think, 1983.
The '79 LRT is a light duty truck, therefore subject to emissions regs.
A 4 barrel carb does not a 340 make.
There is no hard and fast way to find a 340 in a car, but being as how I am intimately familiar with small blocks and how these cars are built, I've sniffed out three 340s that have had 2 barrels installed, 1 in an A-108 van, 1 in a '65 Barracuda and another in a Chevy truck, of all things.
All 3 bought for under $200 each, all ran.
That's not to mention the 340s I've found with 4 barrels in some pretty odd vehicles, like the one in an early '80s car hauler.
If you're digging in an engine or iron pile, the biggest giveaway is a large 4 cast in near the back of the block on '70 and up 340s, as well as an 'O' cast at the bellhousing flange, though some 360s also have the 'O', but they have a 6 where the 340 has a 4.
Any stock 340 or 360 head has at least one line on the ends of the head (l), '894, or 'X' heads and '587 heads have 2 lines (ll) on the ends.
Some have a line with a block beside it.
Later '72 and 73 340s come with a harmonic damper that looks similar to an early 360 damper, but has "Use With 340 Cast Crank Only" cast into the face of the counterweight.
All this having been said, if you're going to the effort to find a 340, don't ignore the '71-'74 360s, they are a helluva good engine and usually a bargain.
One thing I do know, if you find a 340 in a J/Y, don't lie to the seller, just call it a "Small block that I want out of this XYZ vehicle."
If they guess what it is and want boo-koo $$, just smile, let it go and look some more, you find one, you'll find another.
Mark.
