I'm assuming this thunderbolt is the early version of the 50 Hp version of mine?
At a very high level, one thing I found when I put PT on mine is that Nos does have a point - Merc at the time made everything bespoke for the engine. For example I now have a box of relays on my transom to work the PT because the relay was bolted to the air box top. The "unique to PT engines and holds most of the rest of the front of the engine on" air box.....
Even if I could be btoered replacing the air box, the wiring loom changed because the relay sits where my cable multiplug currently is. That in turn moved the cable connection down to where my fuel line connects in, the fuel moving across to the other side, which - you've guessed - meant another variation on the case!
Have a look at the online Microfiches - Mercury Outboard Parts by HP / Serial Range
That will give you a better idea of what's needed.
For what it's worth, my Flywheel is a 2 part thing - the hub and the rest. Being reasonably well acquainted with it It would be difficylt to fit a recoil to it. The big Q is does it have teeth for the starter to engage in round the perimiter?