My opinion...
If I was going to construct another "fully stacked" amiga, I would definitely do it with an A3000... everything in the original case. (BTW, for $3 you absolutely scored. The A3k is a *really* nice machine.)
Keep the A1200 in its desktop case + B1260, and use it for AGA demos... then you have the best of both. :-)
About your Blizzard -- certain mask revisions of the 060 do run a little warmer than others. Mine did, though it was still fine at 66 MHz with a little 486 cooler + fan.
