Nitro/ Heavy shot Mag Blend
 

I am a Nitro user 301A out of my Browning Invector Plus with 26 in barrel and Kicks 665. But they dont make the 301A anymore. Is the Heavy shot Mag. Blend as good as the Nitro?

No, but it will give you some good patterns none the less.
On a side note, and you might already be aware, but that Kicks choke is not rated for heavier than lead shot.

You will have to repatten your arm but the mag blend will do the job maybe not quite what nitro got but it will work fine...