working on some SR heads. Considering using some 55* cutters that I have used on Big Duke Brodix heads before, but they have Beryllium seats and titanium valves. Thoughts on using on standard Indy stuff before I wreck something? Maybe no valve margin after cut? I think I am already starting to talk myself out of this one.

I have never messed with 55 degree seats on any head that did not have titanium valves and beryllium seats. I know they flow more at higher rpm and less at lower rpm. If you are not going to spin it over 7,000 rpm, they are not worth the cost. But the higher degree valve angle is harder on seats, and the light weight titanium valves help the seats survive.
http://www.dragzine.com/features/valve-seats-will-50-55-degree-angles-work-engine/

I've used a 55* seat many times. I now would only use it in a blown application or something with a ton of nitrous.

For the N/A stuff I use the 50 almost all the time.

Also, the flatter the port angle the less effective the 55* seat is. As you stand up it the port the 55* gets better.

Now that I've typed all that I would probably still use a 55* seat on a N/A application if the port angle was high enough to get the SSR back in shape.

Significant effect on the effective flow window during OL (since lift is low), should do better with 1-2 degrees less LSA.

I'm no expert. I don't think there is any useful benefit until you get over .800" lift.

I'll have to see if I put a 55* on a spare valve if it will even leave a margin. 50* looks to have a lot of options. Guess I'll have to experiment. I was just wondering. I know there is a lot of variables bowl shape and such. Also somewhat concerned about durability. A freshen every few years ain't so bad.

Not true.

I also forgot to mention the under head shape of the valve. It's critical. A nail head and steep seats don't like each other. The steeper seats are also tougher on valve faces so you want a good margin.

the Indy valves are very thin on the seat face area. I don't think they would even take a back cut of significant width.

Correct Rickseeman 👍👍👍