hi Apache1
i also went the same route to build up practice, i got a new window rubbers from classicparts and reinstalled the same old glass
it's much easier with two people, someone can hold and push agains the glass while the other pulls the string and uses a rubber hook tool to set the rubber in place
tho it is possible to do alone, with a big rubber suction cup, but i would not recommend starting the job single person, one slip and glass falls

with 2 people, it's not too difficult, by the time you are done you will be an expert

i recommend you google how to do it and watch a few videos online first, their are a couple good ones floating around for that specific window.
that way you can have a good understanding how to pull on the sting to lift the rubber lip over the metal
i used plastic bailer twine for my string, it is very strong and you won't worry about pulling so hard it will break, the twine will tear that gasket rubber before it breaks.
best of luck, you can do it!
-s