Have a look round the PCB - are there any extra diodes for an ISO key next to left shift or maybe an unused split backspace option? You could use them, if you can get them off.
If not keyboards are not high voltage or current so the only thing you need to worry about is the size, if you want it to look perfect. Hopefully they're not tiny and a ruler or tape measure will be accurate enough to measure them.
Common Passive SMD Package Details
SMD Package type Dimensions
mm inches
2920 7.4 x 5.1 0.29 x 0.20
2725 6.9 x 6.3 0.27 x 0.25
2512 6.3 x 3.2 0.25 x 0.125
2010 5.0 x 2.5 0.20 x 0.10
1825 4.5 x 6.4 0.18 x 0.25
1812 4.6 x 3.0 0.18 x 0.125
1806 4.5 x 1.6 0.18 x 0.06
1210 3.2 x 2.5 0.125 x 0.10
1206 3.0 x 1.5 0.12 x 0.06
1008 2.5 x 2.0 0.10 x 0.08
0805 2.0 x 1.3 0.08 x 0.05
0603 1.5 x 0.8 0.06 x 0.03
0402 1.0 x 0.5 0.04 x 0.02
0201 0.6 x 0.3 0.02 x 0.01
01005 0.4 x 0.2 0.016 x 0.008
You can also bend the legs of a standard DIY keyboard through hole diode and solder them to the pads if you don't have a window in the bottom of your case