Then you'll have to find a watchmaker to cut the old stem, re-thread it, fit an adapter, cut the new stem and possibly re-thread it , then carefully measure and adjust the length to fit.
Which is all possible - but it will cost you a lot more than a new crown and stem.
It might be an idea to email Rob at monsterwatches.nl He does this type of thing regularly and may be able to offer a different crown/stem to fit, which could keep your old monster looking more original (if that's the issue).
I personally like the newer knurled crowns look, but it's your watch - look for SRP309.
I do this pretty regularly since almost everything I buy is missing the stem or has a broken stem (I bought a lot of stems from Ramon last year, very helpful). I picked up large bore hypodermic needles from a feed/hardware store (for putting medicine into the butt of a horse) and I use those to make the collars from. If you can't thread them you can get the stem halves to friction fit into the collar and then use loctite, solder, or even glue. Divers are tricky since you need a short collar so that the crown will screw in, but you can still get by with loctite if you aren't able to thread them.
What a great solution.
I grew up in Redditch which was/is the UK centre for needle making they still have an old water mill where some of the first were manufactured.
I'll be off to a local farmers suppliers this weekend for some sheep injection spares.
Over here there is a 2 part speed epoxy made by deluxe materials which sets in 60 minutes which I'll try.
Yes Ramon is very helpful.
Many thanks for the tip,