Flathead valve spring compressor from Princess Auto Ltd. part # 2918456 cost was $23.99. Tool works great after a small notch made in arm so to fit around block allowing screw to seat squarely on valve face. see picture.
Were any of your valves stuck? I have gotten the heads and intake manifold off of mine, and about 50% of the valves are stuck. I can turn the crank and all the pistons move but not so with the valves. Not bad for having sat outside for 15 years.
I've gotten lucky all the valves are free, there was one valve that jammed when trying to slide through guide but found it had a little lip around edge where valve contacted lifter, just cleaned up edge and then it slide through no problem. I haven't tryed removing any of the valve guides yet, hope my luck still holds!
Sears makes a cheap one that's about the same size and shape as that one but with a standard lever action clamp that works really well for flatheads. I think it's about $20 too.
****! I didn't even think of Sears, I will keep a mental note to check for tools there before the further drive to Princess Auto. Thanks!