Question about the price of 340s

I got my red headed stepchild low compression 73 340 attached to a 904 for $400 many years ago and I saw a 69 340 for sale on Facebook today for $3000.
Im not sure, but I was thinking. If I was around back in the day, couldn't I take one of them late 340's and slap a top end from another on and have an 'early 340' basically?