"LA" was an engine type, the 318 and 360 are example of LA Blocks.
The Dodge Truck V10 was (is) based off the 360ci LA Engine. Dodge needed more power, it was cheaper to modify a current engine, then to design and build a new model.
Dodge took the current 360 LA engine and added 2 cylinders.
The V10 was designed as a torque truck engine. only later was it modified for a concept car, known as the Viper.
The Viper Concept was a great smash. Dodge got the concept car into production in record time.
It's quite common for people to think the V10 was a performance engine first, when in actuality it was a hard working truck engine first.
The LA engine design goes back 40 years, released in the early 70's.