Econo Heads

I was checking out the TTI exhaust website, about ordering my exhaust and headers. I have a few questions for some of you gurus out there
in Mopar land. What in the heck are econo heads and they also mentioned
something about an LA bolt pattern or something like that on the heads.
I don't want to order headers and they send me the wrong ones.
The car is a 70 340 duster with original everything, and it was built at the
LA plant. Thanks, guys :thumleft:

They're referring to the econo W2 heads. LA refers to the 273/340/360 and the later 318(67&up). "A" engines are the 277/301/318(66&earlier).