I get the fit issue. Either the waist will be too big, or the rear will be tight. Generally guys pants don't fit tight on the legs, unless you buy skinny jeans. Some guys (a few) are actually buying girls jeans for this look. I'm not a big fan in guy mode. Look for Dockers with pleats. Yes they will be a bit baggy, but that can be OK if you are looking for a classic 40s/80s look.
You might actually ask the tailor to bring the waist in. In the day, a higher end department store, and certainly even now a men's store would offer that service free or inexpensively. I would think that these stores would probably be pretty safe/friendly.
Good luck and let's us know how it goes.
Oh and BTW, it is expected that any really nice slacks probably need hemmed. Sure you can find off the rack, but if your really styling, you have to get fitted.
