Yes, Alpha Strike Companion is still the source for rules of converting a unit to Alpha Strike. There's a significant amount of errata to the book that you can download from
https://bg.battletech.com/errata/.
There are plans to release an AS conversion/PV calculation "book" at some point, but I don't expect it any time soon.
https://mordel.net has a 'Mech designer function that does Alpha Strike calculations and shows it's work. It doesn't explain how to convert, but is a great resource for comparing your initial attempts at conversion to see what steps/rounding/etc you should go through. Or just doing the conversion for you if you don't want to learn to do the conversions.