Legendary interiors install question

Tight is good. The foam is gonna give away some during the first few months of use. I wouldn't compare new foam thickness to 4o year old foam thickness anyway.
Also, While the seat sections are apart and the back cover is mising they might seem odd shaped. The finished seat should look fine for a long time to come. Only real problem I've had was getting the cover down far enough at the top back to underlap the back panel and not show the binding in those corners.
One more thing... instructions dont tell you how to cut the hole for the hindge bolt. Peck at it with a ball pien hammer until the bolt hole cuts hole through the cover. Produces a nice round hole that is less likely to sprout.
New wear washers there are a good investment too.