Feek 61, there is plenty of reference available on the net. Just type in a photosearch and it will kick tons of it out. The best I came up with for a TD accurate profile was this
I don't know whose it is and I will remove it if required ,but it was out there and freely available to look at when I got it. It seems fairly accurate.
As regards the model personally I think the head is fairly proportional to the rest of the build. I know that Randy updates parts of his kits as the casts wear out,and ,for example, somebody I know got a Blockade Runner a few months after mine and a few parts of the engines were slightly updated to reflect screen accuracy, but thats what the professional casters do. Small improvements are made as the kitmaker gets more feed back and has more time to spend revising them, from what I have seen. As regards the Hammerhead I believe the scale is currently proportional.
In most of the photos, such as the one you've got , the angle it is taken is very deceptive anyway and can be pretty much ignored as a judgement of scale against the rest of the ship. Balls on accurate to the millimetre or not ,there aren't any other kits out there of the Tantive IV that I know of at this scale and I'm quite content with mine.
I'm after the Sandcrawler next ,but I'm waiting for another kit from another builder first. The SD is still in waiting for the FO to be finished,but its the summer and I've had other none model things to do.
PS: I've mentioned this to Randy over an e-mail about the SCrawler . He took his measurements from an original RBR scale model from the original production whilst doing some studio work.So with his strong reputation as a professional minatures builder for both the film industry and the replicas arena I wouldn't worry much.