You are able to use a sample private key created from bitaddress.org if all you want to do is convert it from PEM and back again. https://www.bitaddress.org/bitaddress.org-v3.3.0-SHA256-dec17c07685e1870960903d8f58090475b25af946fe95a734f88408cef4aa194.html

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PEM is an RSA private key file format. So you are trying to convert an RSA private key bytes to bitcoin private key bytes but this doesn't make sense at first because bitcoin private keys use elliptic curve cryptography, not RSA.

But when I ran bc_key with an address in some wallet file, I got this output:

-----BEGIN EC PARAMETERS-----
short ASCII string
-----END EC PARAMETERS-----
-----BEGIN EC PRIVATE KEY-----
really long string of ASCII text that looks like one in OP
-----END EC PRIVATE KEY-----

So what you did is convert the output of bc_key, an ECC private key, into an RSA public key. We should probably figure out how to get the private key bytes out of this ECC key first as it's most likely a valid bitcoin private key.