The valve seats of the RT 1 head are higher in the combustion chamber than the old heads. In other words the pockets that are machined into the head for the seats to sit in aren't quite as deep.
Because of that they have very slightly more compression potential.
The bowl below the valve and around the guide is slightly different than the older version of the head also.
Since the RT 1 head is the only legal head for the LO 206 it is made to very strict dimensions. All the RT 1 heads are as close to identical as possible.
If you want the head that makes the most power for a MODIFIED motor the WF head is what you want. If you are following Animal rules the WF head is not legal.
^ Plus the rt-1 head flows better than any of the stock older cast heads -- partly due to seat height. Some of the older castings still make great small plate heads because the port runner was slightly smaller on them as well.
One other difference you may find between old and new RT1 heads is the older ones could still have the 1/4" rockers, stud and plate. While the new ones have a larger diameter set. You can up grade an older head though.
Remove the chain guard and the air shield that goes over the top of the cylinder. Use a mirror to look between the head and the block and you can see the letters RT 1 on the head.
The letters are backwards because of using the mirror.