he is doing digital to analog ,
only good way is with an analog dash harness , gauge pack
remove dash with harness attached (theres a bunch of stuff to do before pulling one out and im sure theres a step by step list somewhere on the net , do a search) then remove existing harness , install analog harness , reinstall dash and then install the analog gauge cluster connecting speedo cable , check eng lamp and vss to back of speedo
also if you want the boost gauge to work you'll need to remove the hobbs switch on passenger fender and install a two bar MAP sensor and plug in (the wire is already there and will become active once the dash harness is swapped over , and connect the vac /boost line to it
not sure what needs to be done to make the fuel gauge read accurately since the digital has a different sender in the tank.