When you say 14V AC for "lighting, etc." do your loads really need AC? Or can some run on DC?
Many economical options for efficiently dropping DC rather than AC voltage (even if starting from AC as you are).
As for the brute-force diode drop method, I've posted this picture before. About $2-3 in parts and has 8 "taps" adding up to about 5V total drop so that would lower the 18V AC to ~14V AC. As GRJ says, to get some adjustability you could add a rotary switch to select which tap to use. These are 8 Amp bridge rectifiers (diodes) but are readily available in other Amp ratings.
On a side note, it appears Lionel bricks are in quite the demand and might have more "trade-in" value for someone who would use the full brick voltage. So if you are able to operate some/most accessories on DC, you can get a 90 Watt DC-output universal laptop charger for less than $10 shipped from a US seller on eBay. That's about 10 cents per Watt which is my target price for fixed-output power (AC or DC). Here's one that has a settable DC output voltage from 12V to 24V.
Note the side-by-side footprint comparison vs. a 100 Watt AC brick; I don't have a 180 Watt AC brick but assume it would be larger still.