tti headers leaking...

just finished some upgrades to my 340. swapped heads to a 318 with the emissions holes in the exh. ports.( they have been seriously reworked)here is my problem and I hope someone can help. I have an older set of tti,headers
I used a set of fel pro exh gaskets, installed correctly and as soon as I fired it up shortly thereafter the gaskets gave out or sound like they have. are the headers the same for any factory head? I did drill and plug the emissions holes.? when I got the headers initially they came with gaskets that looked to be two glued together.they served me well but disintegrated when I took the motor out.has anyone had an issue with the heads (456s I think) and tti,s. should I double up a set of gaskets like I had initially?the exhaust ports look like the 340 heads as near as I could tell? any ideas?