I fried my On30 Mogul PCB board trying to do what you want to do. I had to make my own diagram by looking at another Mogul and I obviously didn't get it  right. I ended up buying another Mogul.

I don't know if Walther's trucks can be mounted "as is". Are screw holes in the trucks the same or will something have to be changed.
If I was doing it, I would just go with metal wheel sets and not mess with changing the trucks

I looked around on Ebay and it's hard to figure out a price since he only has one car and the loco, plus the track and power. Plus the loco isn't in good shape. People are asking $69 to $135 for locos. The $69 plus $15 shipping one is new.
There is a car with the power stuff for $38.50 plus $12.50 shipping. Prices are all over the board for various assortments of pieces

This is the standard 4-4-0, not the high wheel version. You can pull six old time passenger cars with no problem. You can pull seven old time passenger cars (with some wheel slippage around the tight curve).
Add some weight in the stack and cab of the loco and you can do ten passenger cars without much problem. It can actually do up to thirteen passenger cars on a layout with broad curves

I agree about the second set of piers but I don't know if there is enough track to be able to do that with a basic figure 8.. He might have to add more track to make the figure 8 larger.

You have the loco and tender and one car. It looks like there were five cars to the whole set.

I can't tell you the value but the roof of the loco is on backwards.

This is a neat place. Lots of old cars and some old steamers.

I don't know what they were thinking with the spin the wheel throttles unless for more steps for more precise control somehow. I must be dense but I like the exact control and hard stop to know that I'm at the highest I can go with the standard one.

That was why I went back to my standard E-Z Command. I didn't like the "Wheel of Fortune" throttle.

It's from this guy's post on the If You Worked on the Railroad Facebook page. scroll down to about 3 days ago.
https://www.facebook.com/groups/658047340912711/user/100004926425617/

The same principle applies to model railroading.

I didn't think about doing it on the side that way.

Here it is folded around the elevated inside. This is 5' x 8'.

Here is an oval connected to the over and under with a crossover.