The 7600 shared a case with the 7200, 7300 and 7500 machines. That was called the Outrigger case and it was also used for the G3 desktop.
If I was you, I would find a nice PC case and fit it into that, with an ATX PSU and wire it up to the 7600's power pinout.
It does get complicated because of the rear I/O panels on Macs were part of the case, not a separate detachable piece like on a lot of PCs. There was no standard, Apple frequently changed what ports were on logicboards and the placement of them.
Generally speaking, if the ports line-up with the case, and the logicboard physically fits inside the case, then it's compatible. But some modding might have to be done to get things actually working.
There are some weird scenarios. Like the fact you can put a 840AV logicboard into a IIci case (you would need to cut the case for the ports) but it does physically fit, but the power supply needs a bit of modding to plug into the logicboard in that scenario.
So that's the other thing... Mac logicboards were designed mostly to only fit a small number of cases, as they were each designed for one case only (roughly speaking), and as such, things like speaker headers, power supply connectors etc were placed for that specific case design.
A 650 board fits perfectly in a 700 case, and the ports line-up, no modifications needed.
You could probably categorise models by case design, and in a lot of cases you'll find examples where they are cross compatible.
Here's a rough go from memory...
128K/512K/Plus - logicboards interchangeable between these, power connectors are the same, BUT Plus has different ports - so you need a new rear case OR you chop up the 128K/512K case to make the Plus board fit
SE and SE/30 - logicboards interchangeable between these, only caveat being the SE/30 has a different chassis (and some later SEs) so that vertical PDS cards can fit.
II / IIx / IIfx - logicboards interchangeable between these, share the same case and power supply
IIcx / IIci - logicboards interchangeable between these, share the same case and power supply
Here's where it gets weird... these models use a different style case, but the logicboards will fit into the IIcx / IIci / Quadra 700 cases...
IIvx / IIvi / Power Mac 7100 / Quadra 650 / Performa 600 / Centris 650 - all use the same metal painted case, same power connector/pin out, the only difference being the ports at the back on the IIvx/IIvi differ quite a bit from memory so some jiggery pokery might have to be done there.
So because of the formfactor of these logicboards, you can fit a Power Mac 7100 board into a Mac IIci case. WEIRD.
Classic / Classic II - logicboards interchangeable
Colour Classic / Colour Classic II / Performa 275 / Performa 575 / 550 / etc - these all use a weird logicboard with an edge connector and so boards from any of these are interchangeable. Although I have no idea what happens if you put a CC board into a 575, usually people do it the other way around.
Power Mac 6100 / Quadra 610 / Centris 610 / 660AV - Larger pizza box style case, logicboards can be swapped between these and they all use the same power pinout.
IIsi - This is a lone ranger, nothing else fits in this, just IIsi boards.
Mac TV - Another lone ranger, its a unique logicboard, BUT I am not certain if the chassis/case will take other boards with edge connectors like the Colour Classic and 575/550/520 etc etc. Hopefully someone more knowledgeable can fill in on those.
Quadra 900/950 - big Quadra, you can only fit 900 or 950 boards in here. BUT I have seen someone put a Power Mac board into one, but it required a lot of modding.
LC / LC II / LC III / LC 475 / Quadra 605 - the logicboards are interchangeable as the case bottoms didn't really change, but there is a small power supply difference between the 475 and earlier models.
LC / Performa / Quadra 630 - first model to use this case, a taller pizza box with CD-ROM drive. The logicboard is again one with an edge connector, but strangely I don't believe they support that many other logicboards. I think in theory you can put a 6200 logicboard into a Colour Classic, 575, or a 630, but again I may be wrong on that one...
That kinda covers the 68k era of stuff as far as I can remember, and I am not sure if it really answered your question,... I am less knowledgeable about the PowerPC era stuff really. But the same principles apply. Look at the physical case size/shape, the port orientation, and power/speaker connector placement, and it will give you clues as to what boards can fit where. But do be careful with power supply requirements - even in the 7xxx series of Power Macs, there were power pinout differences between those models !