I used to run a 3640 in the 3000 desktop for many years with no case mods. i simply siliconed a small thin laptop style fan onto the 040 in the center. It had about 1/8th" clearance on top,but did the job nicely and never had any problems crashing or overheating. going to the latest mask 040's can also help. iirc the HRC(HCMOS) versions of the chips ran a bit cooler than XC and RC versions but you should go by the date code and use the newest possible if you intend to change it
