Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
Most universal blocks will fit,GTS 450 has the same mounting pattern as GTS 250 or G92,that should help you finding a cooler. I don't believe there are any full cover blocks for your card.
It should be noted,it's kinda overkill to watercool it,in fact I had an EVGA GTS 450 ,and it's been very quite.
i used an old acetal maze 4 gpu block on my gts450. temp never got above 47c when folding 24/7. same square pattern going all the way back to the 7xxx series of cards. i didn't bother cooling the ram because the factory heatsink didn't even touch the ram on mine.
you can get the low profile maze 5 blocks from danger den for just over $40 still.