Struggling to find mufflers

Walker's catalog is pretty good - look up the Dynomax Turbo style mufflers for diameter, offsets and lengths.

Another company, maybe a little less prone to drone is Magnaflow
https://www.magnaflow.com/collections/performance-mufflerSame deal, look up size, length offset, etc.

Offset should work better when lining up frpom factory hanger locations to the tail pipes.
H-pipe should be approx 20" after the individual tubes end inside the collector.