S9 and S9js are the same hashboard size, S9i is different, it's a bit smaller (the hashboads heat sinks), my information is accurate dating to as far back as maybe 2-3 years ago when I last laid my hands on anything S9, so take it with a grain of salt.

However, if you manage to physically fit them, they will work without a problem even with the stock firmware, I still remember scammers putting S9 hahsboards in S9j because the J was selling at a bit higher price, the S9i was always the most expensive among them all because it was unique and they couldn't fit S9 hashboards in it.

There’s me thinking the S9i what’s the ‘top end’ model of the S9 with its smaller heat sinks.
When I searched I was finding answers that stated the S9J was just a standard S9 but slightly overclocked from stock.

I only want the boards to put in 3 standard S9 I have with faulty boards. Seems like a waste now.l….

Thanks.