The Buick Centurion with the 455 engine I am not so sure about. I will go looking for some information on the heritage of this particular engine.
A 455 engine was used in two versions in Pontiac cars for this era:
the standard engine (lower compression) and an HO engine, with higher compression.
The "HO" stood for "High Output". This engine could be distinguished by rectangular , rather than round inlet and exhaust ports in the heads. This engine appeared in the Pontiac GTO for the years 1970 and 1971. After that time, American pollution Laws had increasing effect.
The HO, like the HO Falcon in Australia, had a stiffer, uprated suspension, and wider tyres as standard.
So the Pontiac GTO HO had two reasons for being known as an "HO": - Handling Options and a High Output Engine. The Pontiac GTO HO was tested and covered 12.74 seconds ET for the 1/4 mile, in factory form.
The 455 Pontiac engine was a different design the the Chevvy 454 Big Block. It was a larger version of the 400 cubuc inch Pontiac engine.
Oh piffle!!! A long winter's night beside the open fire, a glass of single malt and a good companion (insert your own preference here) would be the makings of you Styria!
In time you would overcome your fear of a manual gear change and maybe even learn to master a crash box!
I would even be happy to teach you how to slide from one gear to the next without using the clutch.