Hello John,
this is a fairly easy job. The most difficult thing is access room. I was fortunate to have a pit in my previous garage which may make it a little more comfortable. You'll need a small, imperial socket set or (as I used) an offset ring spanner and a box spanner.
Pack the gears with petroleum jelly (vaseline) and use a new gasket (probably came with the gears, anyway) tighten gently then torque to 10-15 ft lbs (I guessed this by hand and experience!)
By the way, I do not recommend fitting the uprated spring in the relief valve as a new, standard one is more than up to the job and if you increase your oil pressure too much then any leaks will be greater! This is especially true on the older engines with rope crankshaft seals.
Regards, John.