hello all,
I have an 87 firebird formula that bought without an engine last summer...i had a 67 327 that i had done up and t-5 sitting in the garage so i decided to put them in i tore the engine all apart replaced alot i replaced the entire bottom end and put a cam and intake on it and ported the heads. everything went in good fired right up let it break in. ran like a top for 3 months and then it started making a clattering noise it sounds like its in the heads on both sides.....i brought it to 3 different auto shops and they had never heard anything like it before...i thought it might be the lifters so i replaced them, didnt help iv replaced the most valve train and pulled the cam but nothing seems to be wrong. someone told me it might be the valve spring retainers any ideas??? it really annoying me!! and it wont clatter at idle it has to be in gear going down the road and it starts to clatter at 2000rpm my specs are

67. 327cid 2 bolt main
stock 1.94 powerpack heads
eagle street and strip rotating assembly with 0.30 flat tops
lunati voodoo 262 cam
edelbrock preformer intake and thunder series 650cfm carb
headers
1.6 roller rockers