这里the highway to意思是.的途径,方法,道路,to是介词
用法是the highway to后面跟名字或者动名词都可以
所以本句的主要结构其实是
The items helped him find the highway.
如果按你说的后面跟原型的话,变成了
The items helped him find the highway to do.
另外举个例子：I find a pear to eat.我找到一个梨用来吃.
find sth to do.可以理解为是找到了某物,并把他用来.
放你那句句子里面就不通了
很难说明白.还是靠语感吧