So the magpul won't clear the dong, will the steel mag clear? You looking for 20s or 30s?
Knowing the country of origin of your steel mag would help. Posting a pic with any stamps or marks might provide that. If you don't know, I assume Romanian since that's where it was built.
So if you're looking for more steel 30s I'd try some Romanian, but offhand I don't know who has them right now. Last mags I got were Hungarians from SGAmmo, not the cheapest but like new quality for $16 a pop.
AIM Surplus is a good source for surplus mags, and still have some of those Polish surplus mags. CDNN also ran some great deals on surplus Romy mags in the past.
Just be aware that these surplus mags come over in lots. When they're gone, they're gone. There are also new production mags like the Croatians but they don't seem to be as heavy a gauge as surplus.
Although I prefer the steel mags I have some Magpul MOEs (the ones with the plastic rear lug) in 20s & 30s that fit my WASR fine. If your Magpul has a steel rear lug it may be the first batch which Magpul admitted was made a little larger than the MOEs.
IMHO a loose fit is better than a tight fit. I've seen some swayin' mags that ran fine. Tight fitting mags are slow to change out for me. I've filed a few of my steel mags down to 'smooth them out'. So I'd focus less on where they came from and more on condition.