It looks like it has a 58 tank, but it looks like a Chief tank. The front fender lamp is early 55/56. The engine number would give a better idea than the frame for dating with the information I have. The frame number indicates closer to 1957. Most parts indicate it is a 700cc Trailblazer model, ie the front fender/wheel, headlamp, & casquet.
The bike is missing a few parts but should still be valued around 4500 bucks more or less with the side hack. The sidecar looks like it was added. I havn't seen any RE Indian's with an original sidecar yet. I doesn't mean there aren't any, just means they are basically unknown. The sidcar fender is different that the RE sidecar fenders of the period. Pricing is always how much the highest bidder is willing to pay. My first Trailblazer was in about that condition and it only cost me 50 bucks in 1980. Sidecars hold there value pretty well and that one would still probably fetch more than a 1000 bucks by itself, if complete with fittings & accessories.