Sir, at the end of the day, as a car enthusiast, it is perfectly acceptable to do whatever you think is right with regards to your car...purism, or not.
To my mind a "restored" car is one whose numbers match. Which is correct to the tiniest nut and bolt and washer and bushing. Given the fact that these engines and moving parts and body panels are NOT available here by any means, then, I would venture to say that pretty much every second "restored" car you see in Pakistan is actually a restomod anyways. What enthusiasts will do, to keep these vehicles running, and sometimes, what they do just to improve performance or efficiency, or just to have fun, is nobody's business but the owner's. On that score...all power to you!
If you're planning on much modifications to the wheel/tyre sizes and the stance of the car, it might be a good idea to purchase them and involve them in the panel work / denting phase. Finding out that oversized wheels chafe and rub against the inner wheel wells later, can lead to costly modifications, which could easily have been incorporated earlier. If your '56 is a complete car (dented and painted, etc), you may find this to be a problem.
A definite thumbs-up for the power steering. Not all of us are endowed with a set of upper arm muscles that are required to wrestle a 25 foot long beast around sharp corners.
And it's fairly easy to keep things "looking stock" by using the original steering wheel over the modified steering column.
Re: Body Work. It's always a process of great tedium. But the idea is to keep plodding away until it all gels well. From what I see, the body work on your Merc is coming along well. I wish you all the best of luck in taking it to its logical end, Insha Allah.