Right, I do this for a living.
You’re making your life difficult !
The drawers are the expensive bits in a 4 drawer unit. The carcass costs pennies.
The carcass will be a standard width (probably 400 / 500 / 600mm)and is pretty much nailed on the be 720mm tall and about 570 / 580 deep including the service gap behind – this bit is important if you do actually have pipework etc behind !
Get down to Howdens (you may need a friendly account holder to do this for you) / Wickes / B&Q whatever, and buy a whole replacment 4 drawer unit in the cheapest door front range – another area where the money racks up. This guarantees that everything will fit together.
Bin the drawer fronts you just bought but use the fittings which came with them to use on your existing drawers.
Presto Hey !! Done.
Note : The more you spend the better the slider / fittings etc will be. See previous comments re Blum.
Phil.w – fair point re ebay. – same points apply though.
Pym