Be careful not to bend the pins when replacing the cpu. Get a passive heatsink using the whole area of the ceramics, fit it in place with some thermal conductive but electric insolating compound. The heatsink should be fixed with some sort of clamp, too. In case you have got a 40 MHz rated 68040 or you do not mind to overclock, look at the following thread as well: Price Drops on Mac goodies for sale... plus free disks!, where TylerEss and DavidB kindly adverted to instructions about overclocking the LC 575.