Birdhead grips on a 1858 Remington

[Kent Hitnuttin]

Howdy, Doing a bit of smithin on my 1858 new armies and saw where a couple pards been doing bird head grips.  That a legal mod to shoot with?  I know the rules say you can on SAA, and technically there SAA's but would like to make shure fore I start cuttin and welding em up.  Plan on shooting classic cowboy and  frontier,  all BP.  Thanks