first welcome to the ford club.

richard swart is correct, even if the ports are raised 1/8", areas that would not normally make contact, may make contact.

i went through the same thing, 68 torino 351w toploader 4spd, started with hedmans 88300s, they worked fine but the world jrs were a little different than stock and one tube on the drivers side bumped the firewall. tried both of the hooker brands, comps and super comps, and some other knock off brands. even the super comps had issues with steering linkage. i was told that this could be corrected by cranking on the tie rod ends. felt like that was going to cause differing turning circles. eventually went back to the hedmans. i have heard other high end brands fit better. you might do a forum search. i purchased the different headers from summit, them shipped them back. had to pay return shipping fees though. but i got to trial fit. however it kept the car apart for several weeks.

another thing to look out for with the taller 351w block, it tends to pull the headers up closer to the floor board and cross member. i think i took pics, i'll see if i can find them.