I have looked a You-tube videos where the presenter just used lots of sealer.-----Little did he know that he was plugging up an oil recirculation channel.----If it says ---NO SEALER----Then they mean it !
The 3 cylinder 25 / 35 was marketed from 95 to 2001 I believe .---Long shaft had a 5" spacer.------The 2 cylinder 30 / 35 was made for many years.----The 2 cylinder 35 did not leave the factory for all years , with a 5" spacer as far as I know.
Short shaft in 40 / 50 / 60 HP motors is not very common.----Those 3 cylinder 35 HP are more common in short shaft.---And they do have the 5"spacer when leaving factory as long shaft..
Check the flywheel key.----A 1985 model has a choke.----Look and see if choke plate is actually closing.----Or put 6 drops of fuel in each sparkplug hole .---Install plugs.----Pull recoil 10 times.----Report what happens.
Remove gearcase first.----Long shot that something is wrong there.-----With it nearly making a full turn it sounds like a piece of metal is loose somewhere.----Remove heads as stated.-----New to you motor ?