I am putting together a 53 tri pacer, the previous owner had the sets redone. ( new foam and covers.)

I put them in after finishing the head liner. yeah i wanted to climb in and make airplane noises.

Now i am 5"11 and i could not sit up at all. my head was trying to poke through the head liner by almost 6 inches.

I pulled the seat back out and i think the issue is was to much foam on the seat base. There is 9 inches of foam there.

how thick is the factory seat foam?