Consider using 25:1 for the first start. 50:1 is f*** all oil really.
IMVHO, wd40 is great for freeing stuff up, but not a great lube in a motor. I'd squirt a bit of 2 stroke oil in the bores.
Also give it a good squirt of 25:1 down the carb throats before attempting to crank it at all.
(Basically, make sure all the internal bearing & rings are well lubed before attempting to start).
And make sure you've got a reasonable degree of confidence the carbs all working OK before starting it - blocked jet means no fuel means no lube to that cylinder.