Pre Hijack :-
If your 1766 is built on a 1600 TP base then use W8AC as per stock 1600TP
The plug you listed is for T4 engines of 1700, 1800 and 2 liter capacity
Post Hijack :-
If your engine builder says "use long reach plugs" then it means the engine was built with later mexican heads which have a different casting, use a longer threaded hole for the plug and hence need modern type long reach plugs. Using short plugs will make it run like a dog.