Nelson, if you do a search on here for any of those heads you will find some posts that might answer some of your questions. Some have had good luck with the 993.
I was told by a Division 1 tech official that the 487x is accepted in place of the 487.
Also, check the for sale section...there was a bunch of 350/270 stuff for sale.
http://classracer.com/classforum/showthread.php?t=56482
Good luck.