I have an old 80s 90s Migatronic 5000MX i would like to convert to gas less, i have a sip which is a simple terminal swap from the factory, 1. but what is involved in switching polarity in the 5000MX, and anything i need to look out for when changing the polarity.? 2 . Do i need to change polarity , i never fully understood the significance of this aspect of gas less Conversions.? 3. In my small sip it takes small gas less wire spools but the 5000MX is currently on 15KG solid wire, i see 4.5 KG spools of flux core on the Internet is this the biggest size spools generally available ?