318>383 swap ('74 Valiant)

383 is a B block, {413/440 are RB}
273/318/ 340/360 are "A" blocks.

You will need a different tranny, 727 for Big block,
different exhaust, different pulleys, brackets for power steering/ alt. etc.

A 360 swap would be easier. That still needs a little research.

Mopar used different bellhousing patterns Each; for Slant 6,
small blocks, and big blocks. So swaps are more work.