Hope this helps.
There were different rocker arms used for different big block applications over the years. Here's the deal:
"no marking" rockers-----these are most likely aftermarket pieces. Most aftermarket are unmarked. However, I believe that they may also be GM #3860305 which were used for 1965-72 non-SHP applications;
"L", "Z", or "X" tip marking----GM #3860308. Used for 1965-69 with SHP and 67-E69 L-88. Also, replaced the 3860305 for SERVICE effective February, 1972;
"M"-----GM #6258611-----used for 1973-74 all big block. Also, became SERVICE for 3860308 effective Novemeber, 1972; currently replaced by GM #10112680
"H"-----GM #3959182---used for L69 L-88, all 1969 ZL-1 and 1971 LS-6. Currently replaced by GM #12368082 which is a kit which includes 1 GM #3959182 rocker + ball and nut.
There was no "N" that I know of; you may be mistaking a "Z" or an "M"
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