While messing around at the salvage yard years agoe I found some rocker arms that measured up and work well in the 201/226 allis engines.  Rocker arms from the International 361 and 407 diesel engines, 806-1206 type tractors offer a higher ratio and fit the Allis heads with little work. It's been years since I put togather a set and I do not rember the ratio.  Hone them just slightly on a pin hone to fit the Allis shaft is the only real work involved, the rest is just checking and makeing sure your rocker arm geometry is correct.

 

I'm going to grab a set shortly for a D17 we're tuneing  up,  and I'll measure them up and post the ratio sometime.