Y-block crank/power steering pulley?

I have a quick question about the crank pulley on Y-block engines. The standard pulley is a single groove pulley. was the optional power steering pulley a double groove pulley or was it a 2nd pulley that bolted inside of the original crank pulley? Thanks for any help you can offer.

 

the one I am looking at looks like it would just bolt inside the harmonic balancer/crank pulley. I just want to make sure I am correct before I buy something I don't need.

 

Factory deal was bolted inside the stock single pulley .

.

 

Thats what I thought...I just wanted to make sure. thanks for your help

 

Throughout the sizes of Y-blocks, I think you will find them both ways (bolt on and cast as a double groove) and a 3 groove unit, depending upon the cu in, aplication, passenger car, Thunderbird, truck or stationary engines. The 3 pulley may be one bolted onto a cast double. Google Y Blocks Forever and search that forum.