I have to replace my Steering Head Bearings and I was wondering if I should use genuine or aftermarket ones.
I'll also be doing the the fork seals at the same time.

Hi there, regarding the Steering Head Bearings I have not tried to find aftermarket replacements, but for the seals, could not find the correct size among common offer, only from aftermarket motorcycle spares suppliers. And the price saving from the original was so small that I considered the risk wasnt worth it, specially if you think that the original ones lasted almost 25 years.
Hope this helps
Best regards
JAP

You can get good aftermarket bearings the NTN 4T 320/28X is a good replacement and Koyo also make one as for the fork seals experience of my own and from others here says buy genuine but whatever you do DON'T buy from Pyramid Parts for either as I am in the process of changing the bearings I got from them and replaced the forkseaks sometime ago as one actually turned the seal lip inside out on a big pothole.

After market headset bearings work well , quarter the price , but buy OEM dust seal as the kit seal is way too much work .

I am grateful for RickG's post #3 cautioning about the poor quality of Pyramid bearings. I'm refurbishing a K1100RS steering stem from a supply of 4 Pyramid's I bought years ago (still in good condition when I opened the cardboard box) I fitted one as the replacement top bearing. Two things I noticed: 1) after fitting and packing with grease the bearing feels gritty and sloppy, not silky smooth; 2) The stamping on the Pyramid bearing is 320/28 not 320/28X. It seems the Pyramid offering is missing the magical X-factor! I'm junking the Pyramids and purchasing either Japanese or European.
Had a Titanic battle removing the bottom bearing from the base of the shaft. No joy with heat or my hydraulic press. Eventually got it off by carefully cutting 2 bits off it using a Dremel type tool with a small metal-cutting disk. My cuts were in an inverted V-shape. I then broke out the V bits using a cold chisel. Bastard of a job.

Easiest way to get the lower cone off is to drive a knife blade under the bearing then get a thicker wedge then a couple of small Tyre levers and it comes off quite easily. I have just done a K1100LT and worked fine.

I tried the Knife and tyre lever method without success - I got no movement of the  bearing cone when driving the knife in. The bearings I eventually removed appear to have been the original FAG bearings fitted at the factory in 1993. The surface of the stem tube and inner bearing cone surface had some dry deposit on them which appears to have caused some resistance to my attempts to remove the cone. 
I had a chat yesterday with my neighbour who has worked on heavy machinery for many years and has removed many bearings from shafts. He said his standard method is to use a stick or MIG welder and run a circle or two of weld around the outer face of the bearing cone and they then are easily removed. He doesn't use any other technique.

I use that method on really recalcitrant bearings. Just wait until the whole assembly has gone completely cold - as often as not, the bearing just falls out. It's also safe to use on a bearing in an alloy housing as long as you have a relatively steady hand.

I have a chunk of 10mm diameter rod that is peened out on one end from being hammered on.  That slight spread of the end can be held in the small space between the bearing race and the head.  A few minutes of tapping around the race with the rod will push the bearing down far enough to get my tire tools in the gap to lever the race the rest of the way. 

A little time with my heat gun on the steering head helps loosen the race in the head.

I have an excess of 5mm and 10mm brass rod and just cut to size and tap evenly around the lip.  A 2lb hammer helps.  

I have used the welding method once in the past.