1977 T/A eng question

I have just purchased a 1977 Trans Am that I know to originally have a 400 engine. The person whom I purchased the car from said he installed a 455. The # next to the distributor is 485428 with a YC stamped on the R/H side (is it a 455?). Also the casting # on the heads is 8221 with B 9 6 10 casted into the exhaust runners,will it be worth doing work on these heads? Or should I look around for something else. My intensions are to build a 400+ HP Trans Am.

Yes its a 455, 1972 - 1974, if you needs parts, just mention any of those years '72 - '74 all the parts are the same. The heads are off a 1971 Pontiac 400, 2.11/1.77.... 96cc. Those heads are good. About middle of the road performance. Too bad those aren't X series heads... you wouldn't ever need anything bigger. But, if you want 400+ hp, you might want a different set of heads. Finding some old X series heads would be ideal for your project. I don't know how much those are going for anymore, if they are even around now a days. But those are the heads you want if you want power.