[Andrew]

My experience with worms and worm gears is that you often have to replace them as a set. The lead angle on the worm+worm gear is usually a custom number.

So, be careful trying to mate a "Stock Drive" worm with a "Boston Gear" worm gear of the same pitch, leads, and number of teeth.

My advice, look at your pitch distance between the worm and worm gear, and buy a set with the same gear ratio and pitch distance.

The next issue, if you failed the original system because the shaft was deflecting (cast iron gears throwing teeth?), you will probably fail the steel system in "low cycle fatigue". In other words, if you passed the ultimate strength of cast iron, you will probably be at a significant fraction of the strength of steel that, after 20-50 cycles, you will fail the steel gear due to fatigue.

I'm assuming that your shaft was not doubly supported, over a short length. You might want to consider a redesign (not sure how much time you have) to get that shaft better supported and therefore remove the chance of failure.

Good luck and sorry that I only have cautions and not much positive,...