I would suggest that you read a lot of the posts already on this forum - your questions are the most commonly asked here, and there is a wealth of information available for you to browse.
Put simply, the Enfield is not a freeway machine, and cannot be made into one. I am not sure why the frame that can drive half up Everest would collapse on the freeway, but the engine wouldn't like it. It is a machine that likes to travel at 55 - 65 mph, with emphasis on the lower speeds. IT will do this on roads less traveled happily and safely - for round town it is perfect, has sufficient 'zip' to get out of the way of fools, and is a very stable and forgiving ride.
But, it will not, and cannot adapted to take 75mph trips on Arizona freeways. If you like the WWII type bike, ride around at WWII speeds - the British Enfield Army Dispatch bike would tear around the war zones, at about 55mph. They would do it all day, but if the squadie riding it opened it up to wot, he would blow the engine - they just do that.
For a period type bike, that looks good, is tough and can cope with dirt better than any other street machine, look no further, and get an Royal Enfield - but don't take it on I 10
There are plenty of places around there, that I have ridden my bikes - until July, I was in Tonapah (exit 94) west of Phoenix, and rode hundreds of miles around there, at speeds up to 60mph, with no problems, but I knew the limitations of the machine, and never considered getting onto that mad interstate - the bike could not do it.