See the guide that is linked to in my signature line. There is section on sizing near the end of the article. With your height and chest/back measurement, you will probably always have problems getting a coat to fit.
Yes, a simple job to take the sleeves up and make them shorter. If you are wanting to lengthen them, that can be done as well if there is sufficient material inside the cuff. May cost $30 to $50 by a tailor and maybe just a bit less by a seamstress. Depends on where you live of course.
Don't know of any shop anywhere that has a good collection of WWII pea coats. There is an Army/Navy surplus store in Manhattan that has a good collection of pea coats. I have given the address and directions to the store in another post, but don't know where the post is.The name of the store used to be Kaufman's Army Navy Surplus. It is now KSI, and the store is in midtown Manhattan on 319 West 42nd between 8th and 9th. The phone number is 212-757-5670.
Most peacoats have only a thin rayon type lining. Normally, the lining isn't for warmth and adds nothing to the thermal retention properties of the coat. The thick outer wool is what normally gives a peacoat its warmth.I agree with Dbear that the hype factor is reflected in the price. Nor am I a fan of the peak lapels.
For an idea of how to get the proper size peacoat, read my guide, the link to which is contained in the my signature line below. The sizing section is toward the end. A peacoat should not feel tight or uncomfortable at any point, unless, of course, one is looking for an extreme fit.
You might call Sterlingwear and see what they say about the sleeve length on the XL. They have a pretty good customer service department.
Our member ClarinetPlayer purchased a MilSpec coat about a year or so ago, and was quite pleased with it. If you have questions, I am sure he would be happy to answer them. He mostly hangs out in another part of forum, so you will want to send him a PM.