norton dominator head

I have two heads for my dominator can anone tell me which one is correct I have one marked T2225U and the other T2225T is there a difference ? my bike is a 1957 "99" 600cc

The markings on this era heads was discussed on the NOC Forum a while back, and the conclusion was that no one actually knows
what all the various markings mean - they are not documented anywhere, and if there are any differences they are not immediately visible.
They may just be batch or mold numbers and be otherwise identical ?

Do they visually look different in any way ?
The best suggestion was to measure the port sizes and combustion chamber cc,
and select based on what you find.

Earlier heads had less finning, and more is definitely better.
Later heads have more inlet port downdraft, but not suggested for the 99 dommies ?
as the bottom end wasn't as strong as later bigger journal cranks.

Got a pic of them ?

http://atlanticgreen.com/nhth.htm

This is abou the best info you will get and maybe the pictures will help if not the numbers