Poly Engine what was good/bad about it and why is the LA better?

yes, I had one of the manifolds years ago, 290 hp.
I has been said that is the the engine in Christine {demon car} is a 290 hp dual quad poly, watch the movie closley it is a 4 bolt valve cover BB (probably a 350 , i believe first year for BB was 58. there were some b engines that had factory dual quads. The only one I can think of now is the 383 343 hp, with dual carter AFB

Yes, Christine's motor was a big block. That's clear from some of the pix.

Don't know if the movie car was original in any way, but the optional motor for a 58 Fury was a dual quad 350 big block (as you say, first year for the B motor) with 310 hp. Standard motor in 58 Fury was the dual quad 318.

High performance 58 Dodges and DeSotos had dual quad 361 big blocks. Dodge had 320 hp, DeSoto somehow got 345 out of the same motor.

In 58, Chryslers still had the early hemi, with 392 cubes in the New Yorker and 300; lesser models had a 354 poly, which was a Chrysler hemi with poly heads. No relationship to the Plymouth 318 poly, and virtually nothing interchanges.

Can't remember if the 350 inch B disappeared after 58 or after 59, but it was soon gone.

The 383 appeared in 59. Had 325 hp with a single four barrel or 345 hp with dual quads. Dodges and DeSotos only. Top Plymouth motor in 59 was a 305 hp 361 four barrel. Next option down was the 260 horse four barrel 318.

The RB first appeared in 59, with 413 cubes for New Yorkers and 300s, 383 for lesser models. And this Chrysler 383 was a raised deck version, basically a 413 with a smaller bore. It was soon dropped and replaced with the B, low deck 383. Can't remember exactly what year, but by 62 for sure the RB 383 was gone.

Then came ram induction for big blocks, in all sizes. Long ram, short long ram, and ultimately short ram (AKA cross ram).

And then the 273 was introduced in the 64 model year, basically a small bore 318 poly with wedge heads. For Valiants, Darts and early Barracudas only at first, but soon was the base V8 in B bodies.

426 hemi the same year. 440 in 66. Wedge 318 in 67 (in the US). 340 in 68. 360 in 71 and 400 in 72. Last year for big blocks - 1978.