what year 225?

Although - this thread has some numbers that are closer to matching what you posted:

http://www.forabodiesonly.com/mopar/threads/engine-serial-number.125797/

4225 T 312

1974 model year
225 CID
T for Trenton engine plant
312 = March 12, 1974

So maybe, combining the two posts,

the H means 1972
225 is the displacement
T is then Trenton engine plant
but 188??