How to connect sections of black iron gas line?
Replace the whole lot with CSST.
Cut out piping in the middle, disassemble back to convenient locations, and re-connect using corrugated stainless steel tubing rather than hard black iron pipe. Sure, the CSST costs more, but routing it out of the way of your renovations will be much easier. Best of all: because the connectors spin freely you can easily join it up to the existing black pipes at both ends without special tools or obscure fittings.