Hi John, LF Harris makes them. Check their web site for sizes. They seem to be the only ones making them. They don't sell retail, so you'll have to have a retailer order them for you. Seem to be good quality & the rings they come with tend to work quite well.
Be sure to use real break in oil with them.
I actually had a set in my own hands recently at Raber's San Jose, CA USA.
They are often called "unleaded" pistons.
I don't know for sure what the true compression ratio will be with the iron head. It's said to be 7.1:1
Looking at iron head the combustion chamber shape around edges is deeper so I expect them to be 7.1.
I know for sure the alloy head piston is the same blank exactly but is machined around the edge so it doesn't hit the squish band area of alloy head. I'm currently installing these in '69 Bonnie.
I have friend that used these pistons on T140 7.4:1 to very good results. They are the same construction so to speak, but configured for 750. The casting is the same material & interior webbing etc. is the same as the iron head. Bore clearance was set to .0045" to good results. The bonnie 650 bore clearance is .0045 also. That has proven good on several motors.
Again break in oil can be very important. Use Torco TBO 40w. run for 200 miles then go to regular oil. In several cases this combination has given perfect results.
Here's an eBay
link to iron head 7.1.