The story from a dealer who was around when they were introduced goes like this: (BTW, he still has a shop on his farm @ 82 years old)
The 451E was the first Jonny to have .325 chain and was intended to be a professional limbing saw. It did not come with, nor was it drilled to accept a bucking spike. Sort of an early version of what market segment is now occupied by the 550XP and 2253 which should be here in a couple weeks. At the dealer meeting introducing this saw, they filled one up, taped the throttle wide open and let it run til it was out of gas. Then did it again. He said it never sold that well since is was priced about the same as a 621. The one I have was originally sold by him on Nov. 4, 1978 for $329.95. (I got it with the original owners manual and receipt.) It was a little low on compression, so I cleaned up the cylinder and put a new ring in it.
My own evaluation of this saw is that it's not the power that is the big deal. It's a good running 44cc closed port saw, but nothing spectacular. What must have been special at the time was how light this thing was and how well it handled. Keep in mind, we are talking mid 1970's here. So try and think of what else was on the market back then. As I've said a few times here, I think most Jonnys from that era were somewhat ahead of their time and can still be run today without feeling like you are running an older saw. And the 451 because of it's light weight is probably the best of all of them in that regard.
A 52E or 49SP is a better choice as a firewood saw, but the 451 is a special little saw just the same.