Okay...narrow gauge...passenger cars...scratchbuilding...I have to get into this thread...
Several things first:
The WP&Y is a narrow gauge road...and therefore...no prototypically accurate items have ever been (or will ever be) offered in standard gauge. But...Sn3 is very close to HO in size...if you like the size. Some people do, very loosely, model narrow gauge prototypes with standard gauge equipment...but they are a minority. Numerous items have been released in the lettering of narrow gauge railroads...but they typically aren't remotely close...such as DSP&P 4-4-0s from IHC...which have almost nothing in common with the DSP&P's only 4-4-0...which was narrow gauge.
The MDC 34' cars are actually too short for narrow gauge cars. They're too short for anything. The lion's share of 3' passenger equipment was 42' long. The Maine 2' cars were 50' long. As was mentioned...they were based off of the Sierra railroad's cars...they're featured in many movies such as Back to the Future 3. MDC's beautiful palace cars are also a poor choice of prototype...the only wooden cars that big...were a set of Pullman demonstrators. That being said...I own both and love them because they look cool.
You could collect accurate stuff...but keep with HO for operation if you'd like...whatever would be the most fun for you.
Here's the mother load for WP&Y locomotives in Sn3...
Locomotives Price List
They offer 2-8-2s...2-6-0s...2-8-0s...both types of diesels...steel cabooses...and freight cars. You also could pick up
Bill's Train Shop's EBT 2-6-2 in either Sn3 or On3...she may have been sent to the WP&Y during WW2...but I'd just get a real WP&Y engine.
I could help you with scratch building the passenger cars...regardless as to the scale (except etched brass Nn3)...and there are far simpler approaches than what I'm doing with my paycar...far simpler and easier...I could provide tips...as would everyone else here...and you would be able to enjoy a cheap approach to adding custom models to your pike.
Btw...CDS is retiring. They also make dry transfers...not decals...which don't have the decal films...but once you apply them...you can't move them around/straighten them afterwards like decals. A successor to the CDS line has been lined up.