318 how much stall

I would never order a "off the shelf" converter. They might be a better price, but a crap shoot on how it will work for your combo. Call any reputable converter company and let them tell you what you need. They might even recommend a lower priced "off the shelf" converter, but you will not know until you ask.
PS: advertised stall speed is a total crock. I have tried two different engines in my car. Everything else the same. Stall speed was about 900 rpm different.