I think you are in the USA. The copyright office of the Library of Congress does some handouts which you may find useful. Basically, copyright usually lasts for the life of the author and 70 years and then to the end of the year. In the USA there are other rules for "works made for hire". Official Library of congress searches are quite cheap ($20, I think) but have from time to time been slow. Once I waited 8 months for one, but I think they are trying to keep more up to date now.

It is true that typographical arrangements and musical arrangements of public domain stuff can still themselves be protected. In the US, a song is usually regarded as one work, so if there were co-operative tune and lyrics by different authors you have a joint work and copyrihgt is timed by reference to the last author to die. This is logocally impossible if someone puts new words to an old tune or vice versa, but I need to research what happens in practice.

In the UK a tune is a separate work from its words.

Step 1 Find out who wrote it and when they died (can be hard)

Step 2 Check if you are dealing with an arrangement and do same for any arranger.

Step 3 If you have a printed piece of music, don't photocopy it. I'd have to check the duration of US copyright in the typographical arrangement but It is bound to be over 25 years and perhps longer, and most sheets of dots fall apart before that.

Step 5 Check what you can do without infringing. In teh US the fair dealing exemptions are wider than England, and also the US haas a "provate purposes" exemption which is wider tahn ENgland. DOn't forget it's "Public" performance that is controlled by copright.

Sorry about the keyboard work.