This kit is what sent KMC broke, they tried their best, but were let down by others who they sub contracted things out to (fuselage moulding), sounds a bit like some 1:1 airliners.
Now if you need or want to fix a few things up, then the worst part is the nose which is quite poor in shape and doesn't capture the Boeing nose at all, a resin replacement was available from Kurt at Authentic Airliners,
I have quite a lot of Kurt's airlines, which are very expensive, but absolutly the best resin kits you will ever come across.
He had stopped manufacturing, but has just restarted with someone new doing the moulding now, so not sure if it is still available.
Another way is to cut the nose of an AMT/Italeri KC135 kit which has a pretty good shape, much better than the Heller 707, or you could just do a mould of that if you are game.