[Fionnbharr (finn:-)]

I believe that the Alabama Forge Council website has modifications to the Kinyon style hammers that they suggest. There are a few videos available on controling your air hammer. You should be able to do a search for both on Google or Ask.com

Design considerations:
-You want daylight between you dies, hand tooling opens up all kinds of possibilities... If you get some videos on flat die power hammer forging, like Clifton Ralph you will understand...
-Bigger cyclinder=larger CFM requirements, unless you use it like Ralph, instead of trying to get it to run like a Nazel;-)
-anvil to ram ratio should be AT Least 10-1, 20-1 is better, and after 40-1 there are diminishing returns...
-If you have to weld smaller pieces together to build up an anvil of suitable weight, it is better to bundle rounds or squares, or even plate along the vertical axis of the anvil, and weld it up. Not laminating a bunch of 1' square drops of 2" plate to get the height and weight you want...
-You CAN run most home built air hammers without a proper foundation, and tieing it down to that foundation, you can use a wooden "foundation", but The hammer will run better, hit harder, and run more "quietly" ;-) if you go ahead and make a seperate foundation for the hammer, and bolt it down securely. It also avoids the hammer wandering off and getting hurt (you or the hammer;-)
-Compressors, bigger is better;-) especially if you want to do some drawing out, or production runs, you can bury a smaller compressor and waste a bunch of time waiting for the air to recharge. With air recievers, again bigger is better, 30gal is worthless, 80gal is better, 200+ is more like it... :-)
-Air lines should be big enough to give you the free air flow you need... Larger hose, and larger fittings, and especially larger filters, regulators and oilers are more expensive but will give better proformance in the long run.
-A large muffler on a bigger exhaust line piped well away from the shop air will be a blessing, again your hammer will run more "quietly";-)
-Hearing protection is still neccessarry;-)
-Use the Blue Loctite, and cotter pins, because an air hammer, especially a hammer that doesn't have a heavy enough anvil, and a sturdy enough frame WILL beat itself to death and nuts and bolts will back out, and it is a bother to have to keep tightening them... Not to mention a safety hazard...

And despite how negative I might seem (although I am not intending it to be...) It is quite do able, and I do wish you good luck... Especially on finding a huge hunk of good steel for the anvil, generally it is better to size your ram to your anvil. I have a 454# axil forging that would make a nice 40# or smaller hammer, Not I want a 100# hammer how much steel can I cobble together to make an anvil for it...

All that being said, I have a Bull 75 (a commecially made utility style air hammer) with a 2" cyclinder. I have a 7.5 hp Quincy Air Master light industrial air compressor with an 80 gal reciever, that develops 22.3 CFM @ 175PSI, I run my hammer at ~135PSI, I have a seperate isolated foundation, an extra 1.5" baseplate, and its bolted down. I have 3/4" airlines and fittings throughout the system. I do not have a long enough, or a bigger line for the exhaust, or a big enough muffler. I can bury the compressor on production runs with my gas forge, but if I pace myself it can keep up by running almost all the time, it is more than adequete for tooling use, and has great control. It is still LOUD and I do have to tighten nuts and bolts on a regular basis, even with all that I have tried to do right;-) YMMV

Goodluck, take pride in doing a good job and work heartily as if unto the Lord, and take pics;-)