This must be the must frequent question of all
Conversions are addictive, No-one has ever had the self-control to do one solitary conversion!
Resurrecting these old sets is a really satisfying hobby in itself and ideal for cold/dark/wet evenings huddled around a blazing soldering iron.
Face it, you're going to be doing a few. So equip yourself with some test gear, it doesnt have to be expensive or complicated.
My suggestions:
A cheapy multimeter, these can be had for £5 or less. Dont bother with a posh one unless you have other uses for it.
Martins 2.4G scanner is quite superb for checking a transmitter's output. Its DIY, but just three ready-made modules linked with a few wires. If you use an RF-Nano, its just two modules linked with 4 wires, it doesn t get any simpler. It costs maybe £3-4 and 10 minutes of your time to assemble.
A PPM meter of some sort, there ara at least three for DIY described here on the forum,
Martins is two modules and four wires. Mine has more facilities but is a bit more involved. Mikes is a super-duper-all-in-one.
...or...
A cheap & cheerful pocket-scope like the one pictured below.
These can be bought for as little as £15, you dont need a posh high-bandwidth scope.
Of course I have a posh scope too but this pocket scope is only 200k B/W and displays PPM perfectly, for £20.
Either the scope or PPM meter will show the PPM stream generated by your encoder and can of course be used to find a PPM source.
The pocket scope can be also used to measure voltages like a multimeter but maybe not quite so accurately.
Hope this is of interest!
Cheers
Phil