the 251 is a great cam...I ran it in a 103 road king and loved it...be aware that this is a midrange cam and will actually make less torque than stock below 2700 rpm...other cams that would make better low rpm power are yuill 14 or t-man 525
I ran the 251 in a 113 build and it was a
good choice, it pulls good!! It might have just a tad less torque than the 255 on the bottom end, but it will pull harder through the mid range and stay on longer as well!!
It will make alittle more engine noise than the 255 does, just so you know!!
If you do the cam change, you should do a SERT and have it tuned of coarse!!
SirMichael