Fabricated welded spindles on a autocross / road race car?

There is not much available for big brakes on my car so I was considering using these Fatman spindles. Should I be concerned with the strength of these vs a cast spindle?

I should add that I am planning on taking the car to some track days and autocross

What car? I'm not familiar with Fatman, but their target appears to be Rod & Custom rather than racers.

It's a 1964 Ford Galaxie, not to many race car parts availible

A steel knuckle whether cast steel or steel plate is better than cast iron or ductile iron. The separate spindle should be forged steel. Call Fatman and ask them if you can see a copy of their engineering finite element analysis of the anticipated stresses on the knuckle. If they don't know what you're talking about then it probably wasn't designed with racing in mind, especially on a large heavy car like that.

I wonder what the NASCAR boys did in period?

I'd do whatever it takes to mount a proper racing knuckle under a car that heavy. Something from a circle track place, not a hot rod place.

Roundy round parts is what you should look at. They are HD and meant for racing. I know that the front suspension design for 1965 big Fords was the basis for NASCAR spec chassis for many years and that included the Chevy PU truck rear suspension.

There are two places in Mooresville NC that sell used racing parts from NASCAR and some of the other racing seris. Some parts are used, some oboslete and some brand new excess inventory. I have seen spindles, suspension parts there. Might be worth a phone car to see if anything might work for you. Both places have websites as follows:

http://www.roushyatesparts.com/Used-Racing-Products-s/108.htm

http://2ndchanceraceparts.com/

I have been there several times and it is really amazing to see the stuff they have literally row after row of racks from components to rolling chassis.

Did you ask them? I have found that whenever I call a parts manufacturer they are very honest about whether their pats will work for your application even if it means they do not get the sale.