You can't. Unless U have a clean room and robotic equipment to remove and replace without tremors that using a hand would impart. The heads are so close to the platter you can't help but scratch them on the platters. Not to mention the precision reassembly and calibration required.
Only an expensive data recovery facility can do this work.
You are talking about gaps and spaces in the microns. Your hand that steady? Going to make sure no dust particles settle in the drive? If the drive is dead you can't make it any worse really so take it apart and see what happens. This is not like swapping out a car battery or putting in a new toilet paper roll.
Why? If you have the same model and everything and you know that your platters are ok, you swap platters with the donor and recover immediately. Do you think that if I give it to a professional is going to save my work?
How do you know the heads are destroyed (original post). A Data recovery service "May" be able to get the data off your drive. Very Expensive and a hard lesson to learn what the phrase "Back up your data" means.
As soon as a tiny spec of dust settles on and your drive starts spinning (at like 90 km/h or so), that dust will scratch magnetic stuff off and that magnetic stuff will do even more damage and so on...
So unless you are working in a sealed room, it is not going to work.
Interesting project you got going on here.
I think your best course would be to grab another HD that is as close to the one that you got, down to the pcb/firmware as you can.
Alot of people here, don't seem to have the experience to know what a hard drive can and can't survive.
I personally had a couple of WD drives run for a few weeks with the cover off, no problem.
There's even videos out there of people running hard drives with the covers off, grabbing the top most head and pulling it off the platter and let it snap back down and the hard drive runs like nothing happened.
Also, make sure the replacement heads are in good shape.
Unless they are new, check the plastic surrounding the metal head part that is in the center of the plastic. You are looking for chips, small ones, and fine black powder like build up. Use a dry QTip to clean.