I had Royal Enfields in the late seveties and early eighties. First one was a 250 crusader, then i ended up with loads of bits and enough to make a 250 continental engine. I took one down to the south of france, and it nearly made it back. Probs included a fallen off (and driven-over by truck) exhaust, fried battery, stripped threads on rocker bolts, all of 2which i solved as i had a ton of spares. Finally in paris the big bearings wore thru, i didn't have spares but did strip it before the slightly shocked breakdown truck arrived to check the problem, and it went back home in boxes.
Under no circumnstance buy a constellation. I restored on of these, paint and chrome and engine with breathers on drive side and off we went, incredible puilling powerr from low revs. But, big fairing and no brakes means rather frightening lack of stopping power. Also my mate's left leg was blathered in a litre of oil.