Having just done a 700 board swap into a IIvx case after trying to put the 700 board into a IIci case and deciding I liked the sturdier and bigger IIvx case better, I can say that the power supplies from all three are the same or near enough that they work without issues. Not sure if they used a different one in the IIcx, though. The IIvx,vi, Performa 600 and Centris-Quadra 650 all use the same power supply, I am sure. My 700 project is happily running with maxed RAM, a 601 upgrade, internal hard drive, and a pair of cooling fans salvaged from a clock chipping kit on the IIci power supply.
I would use a 650 board over the 700. You can get a lot more RAM into a 650, and the 700 board does not have a CD audio plug so you won't be able to listen to music CDs, if that's important to you (maybe if your CD ROM drive has a headphone jack, but not through the system). If I had known when I bought the 700 board that the 650 was the same form factor, I would have bought a 650 board instead of a 700.
Oh, and I wouldn't bother buying a conversion kit to do this. All the parts you need are readily found on ebay or from members of any Macintosh forum like this one probably for a lot less money than you would pay a retailer. There hasn't been a response from Micromac in a long time, anyway. There was a thread about it recently. The website hasn't been updated since 2000, so don't place any orders with them.
I would use a 650 board over the 700. You can get a lot more RAM into a 650, and the 700 board does not have a CD audio plug so you won't be able to listen to music CDs, if that's important to you (maybe if your CD ROM drive has a headphone jack, but not through the system). If I had known when I bought the 700 board that the 650 was the same form factor, I would have bought a 650 board instead of a 700.
Oh, and I wouldn't bother buying a conversion kit to do this. All the parts you need are readily found on ebay or from members of any Macintosh forum like this one probably for a lot less money than you would pay a retailer. There hasn't been a response from Micromac in a long time, anyway. There was a thread about it recently. The website hasn't been updated since 2000, so don't place any orders with them.