The firewall mounted fuse block was on 48, 49 and I think 47.
This is a 49 firewall
[URL=http://s173.photobucket.com/user/mr48chev/media/GM%20AD%20truck%20information/AD%20firewall%20differences%20by%20year/IMG_4386.jpg.html]

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This is a 51 firewall and you can see the stamped ribs Dave mentioned earlier. Just for the sake of comparison.
I'd say that the title was correct for the truck in question. You can buy a reproduction door post plate for 25.00 or so but I am still hunting the correct font of stamps
Big problem is that years ago guys took those plates off when they painted the truck on a regular basis and forgot to put them back on. Up though the seventies no one gave it a second thought.
If the truck has to go through inspection to be registered before you can drive it it might be a bit of a hassle but if you can take that title down to the license office and transfer it and get tags with a new title in your name you are probably good to go,