I have been looking for a sickle bar mower to trim along the edge of my pond as well as cut a couple of acres of grass. I will also be reaching under the trees and bushes along the fence line to cut the multi-flora rose and some saplings to keep the growth in check.

I have found two 7' pull type sickle bar mowers. Both are New Holland - one is a model 455 and the other is a 456. Can somebody help me out with the following information and provide an opinion.

Condition: Both mowers have been stored inside and neither has been used for at least 15 years.
The 456 looks to be in full working condition in that the sickle moves, guards are all straight and in good condition, the 455 the sickle bar needs some work as it appears to be rusted and stuck although I think a little penetrant and few hammer taps would get it loose.
The 455 has mower type guards, i.e. single units with ledger plates. The 456 has a Haybine type guard, i.e. double guards with smooth sides and no ledger plates
The 455 needs some guards, wearplates, holddowns, and probably a new sickle.
The 455 needs a new main lift spring and cable but otherwise looks to be in generally good condition
Pricing - the 455 - $300; the 456 - $500
The 456 is also about 120 miles away from my place whereas the 455 is about 4 miles.

When did NH switch from the 455 to the 456?
What are the differences between the two models?