I used either stranded #6 or #8 wire ( I think #6) when connecting the lugs on my MEP-701a / MEP-016b and don't recall any problem getting them to fit. As to the fuel tank, my generator is in my back yard beside my shed, with a 55 gallon drum full of diesel kept inside the shed using a bung adapter fitting from Hardy Diesel (they have a web page and sell on ebay, have just the fitting or also a kit with hoses, etc.) These adapters are designed to be used with a return fuel line, but you don't have to use them that way.
3 way tap drum tank kit. Two line supply and return!!! | eBay
I then used a 12 or so foot length of surplus hydraulic hose (also off ebay, I think it cost $15 or so) with a JIC fitting on one end and a NPT fitting on the other. The fitting with the screw off cap on the fuel inlet for the generator is an AN fitting, these will mate up with civilian JIC fittings (I forget the size number, may be 1/4 inch JIC or #6 AN, but someone here may know, there are technical differences between AN and JIC, with the AN being rated for more disconnect and reconnects due to the way their threads are cut) I also have a cut off valve inline with the hose ( in case of weed eater accidents, vandals, etc.) and a anti-siphon valve in the other bung adapter hole to keep the drum from collapsing under vacuum (originally I just used a draincock fitting, but decided to idiot proof with the anti-siphon valve).
Ike