Very nice start. You have a 1960 or 1961 Chief, depending on which year it was sold. It appears to have the kidney shaped Matchless tool box on the left hand side that was used starting in 1960 after AMC took over and sold the remaining Royal Enfields as part of the deal. The title on my 60 even lists the name of the bike as 'MATIN' as in Matchless Indian. There are others on this forum that own Chiefs and I am sure will chime in. As to your battery, the original is listed in the 1960 parts book as Lucas #GUZ11E, which translates to nothing currently available. Any 6 volt battery that will fit the box will work. I have two B-49-6 batteries wired in parallel, fits the box, still 6 volt and way more capacity than necessary. Hitchcocks in England (google it) has most if not all the mechanical parts. Luckily you seem to have the original sheet metal, dash and headlight, so you are way ahead of the game in that respect. Wonderful, interesting machine. Regards Tom.