Be vigilant and ask around, the US L code 250 is an easy engine to find because its not a 289, 302 or 351 V8.It differs from the T and B code 200 because the a/c unit and air pump are on opposite sides to the Fairmont/Capri/Mustang/Tbird/Cougar/Zephyr in later model years. The Autolite 11001, Carter YF or RBS carb, low mount starter and the 250's tall build (1.67" taller at 9.469" from the crank centreline) is all you need to know.
Reason there was never an L-code 250 Fox was that in 1980 to 1981 the definative 4.2 liter engine was a 255 Windsor with 112 to 120 hp, and little Foxes didn't have HO's. The little T and then B code 3.3 I6 therefore saw quite a number of Mustangs and Capris from 1980 to 1982. Not that it was much of a turn on, loosing 18 to 24 hp on the little Z code Cologne 2.8 V6.
See
viewtopic.php?f=11&t=47758&p=498915#p498915
Suprisingly, according to the Consumer Guide, the L code 155 hp 250 was an addition from Fords Ranchero pickup during the 1968 model year. The 68 Mustang definately had it on the option list, but I've only ever seen the 68 Ranchero with a US 250.
1969-1970 Falcons and Futuras had it as an option.
68/69/70/71/72/73 Mustangs
along with Monarch/Granada/Versaille/Maverick/Comete
uni body 68 Fairlane/Ranchero,
1970.5 Falcon (a 2-door sedan version of the Torino hardtop)
1969-1971 Torino
some separate chassis 1972-1973 Torinos had 250's.
Although the donk was comparitively rare, if you look you'll find it. If you blink, its easy to miss it. But we did see a 250 in Britian back in 2006.
VikingRob had a 1969 variant from a US Ford Falcon which he wanted to put in a British Ford Capri, it even had an Edelbrock valve cover and engine numbers confirmed it was a Falcon engine.