The IIsi adapter will work. I know this for a fact because I once owned one and tested it in my SE/30 logic board, with the logic board hanging outside the case. I tested with a Turbo 040 accelerator and a MacCon Ethernet card. The IIsi adapter works perfectly in any SE/30. But I was unwilling to cut the metal frame of my SE/30 chassis, so I sold the IIsi adapter for $33 to someone who was willing to cut on his chassis. I ended up buying a Stratos TS Adapter from Manabu Sakai of Artmix Japan (for $175). I now have the TS Adapter (and Turbo 040 40MHz card, with latest edition ROM) in storage and use a 50MHz DiiMO accelerator in my SE/30 full time.
In regards to the IIsi adapter, you also need to consider that even if you make it fit your SE/30, the fact remains that any card you attach will not fit without first removing the floppy and hard disk. The card is very short, and any accelerators you add would be parallel to the motherboard. This is the advantage of the TS Adapter. The TS Adapter is taller and will allow you to keep a floppy and hard drive in their normal mounting locations. The DiiMO accelerator also solves many problems too with its pass-thru connector on top. And even though the DiiMO is a bit slower than even a Turbo 040 25MHz, I have found it more compatible than any DayStar 040 card (with or without 040 cache disabled).
So really, it's a lot of work to get the IIsi adapter to function the way you want it in an SE/30. That's why I ultimately broke down and bought that TS Adapter, and why I later bought the DiiMO. You can see my DiiMO photos here. I mention where they are sold in the comments under the main photo.
In regards to the IIsi adapter, you also need to consider that even if you make it fit your SE/30, the fact remains that any card you attach will not fit without first removing the floppy and hard disk. The card is very short, and any accelerators you add would be parallel to the motherboard. This is the advantage of the TS Adapter. The TS Adapter is taller and will allow you to keep a floppy and hard drive in their normal mounting locations. The DiiMO accelerator also solves many problems too with its pass-thru connector on top. And even though the DiiMO is a bit slower than even a Turbo 040 25MHz, I have found it more compatible than any DayStar 040 card (with or without 040 cache disabled).
So really, it's a lot of work to get the IIsi adapter to function the way you want it in an SE/30. That's why I ultimately broke down and bought that TS Adapter, and why I later bought the DiiMO. You can see my DiiMO photos here. I mention where they are sold in the comments under the main photo.