An Org. in Berwyn has setup up a low cost rental program for air sweepers totally certified by IL-EPA etc. at Jack's Rental, 16th St @ Wesley.
This could allow you to get in and scrape the dickens as you need to which would be way faster than messing around with chems.
I'm gambling that being a 2nd floor bungalow, this was built out after original construction and likely a cheaper pine material that was for whatever reason all the rage in the post war period of growth.
Maybe not, the sill could be original but the casings newer. Either way, I did it without abandon in my attic, and both me and my dog were tested for lead and negativo.
But the Air sweeper, the correct respirator and proper sealing off rooms with plastic and tape, will allow you to get that off with a Hyde 2.5" carbide scraper. The blades are dirt cheap now at Depot for $5.
Hope that helps? They also make a 1" carbide triangle 3 sided version but you should go online for that one.