Definitely the 51-53 rotator type valves. This link shows the three types:
http://www.vanpeltsales.com/FH_web/f...al_tools-1.htm
We rent a removal kit for flathead valves but I think you can get these out with a good quality valve spring compressor. This link shows the kit:
http://www.vanpeltsales.com/FH_web/F...-rentalkit.jpg