I am in the middle of purchasing a 68 with a 427/390 big block, where do I check to make sure this is the original motor?
2nd question: how much should this be worth? the body needs paint

The VIN code will be stamped on the block, passenger side on the front of the block where the head bolts. There is a flat area just forward of the head.
Value is a whole different question, convertibles are worth more than coupes. Condition has a lot to do with it , and how badly you want the car is always an issue.
This months Corvette fever has a listing of recent auctions, Low was a 68 roadster that sold for 23,500. Engine size wasn't mentioned. On the high end an L-89 went for 54,000. L-89 is an aluminum head 435 horse car, pretty rare.
Hope this helps.

Dave, thanks. one more quick question: will the number on the block match the last six digits on the vin?

Yes.
Be aware too that there are many other issues that make a numbers matching car.

Dave, what ever insight you can offer to my uneducated mind on number matching would be apreciated.

ill add something here..

the minimum necessary to make it a numbers matching car are the following..

the body VIN must match the engine, transmission and frame.


engine is where dave told you.

transmission.. I dont know for auto.. but four speed will be on the passenger side of the main housing near where the tail piece bolts on. and the frame will be in front of the drivers number 4 body mount on the upper surface.

these are the only four things that cant be fixed (and they can be but its cheating)

other items come down to date codes and casting numbers.

the date and casting numbers should be correct for the int and exh manifolds differential, calipers, etc.

these items can be replaced as there is nothing to uniquely identify them from any other car made during that time period. you should get "corvette by the numbers", it will tell you the different casting numbers for the different options available.

you should also check the engine & transmission casting numbers just to be sure that someone didnt do a half-a$$ restamp.

you know if they match up that it is either original or professionally forged..

RHeyboer said: Dave, what ever insight you can offer to my uneducated mind on number matching would be apreciated.

What Ben said!!!!!!!!!!!!!!
About the only thing I can add here is be sure to educate your self. Find someone you trust that knows the cars and can go with you to look at the car.
You're getting ready to plunk some serious cash on a car.
Anybody on here near Heyboer that can help??????

You already had some advice on how to educate yourself..

But before you pay any premium for a numbers matching car you better understand what it really means...even the NCRS will classify a car as a matching numbers car even if those numbers were restamped...

You have numbers matching cars , correct cars even thought the numbers do not match, you have fully documented cars which may be correct or may not be...you get the idea...

BUT to be blunt...I never could tell if a car was a matching numbers car from the drivers seat while winding out second gear...and at times like those I really do not care...

Worth is only you the buyer can determine...BUT you better understand that a Good Paint job will run you about 4-5 grand ..PLUS if the car is truely a "correct"
car are you willing to drop a $1000 to replace the radiator with a OEM correctly dated, and numbered radiator or just go to Auro Zone and drop in an aftermarket radiator....

My 64 is fully documented back to the original order forms,have all registrations the car has ever had..etc every thing on the car is Correct With the exception that I put on disc brakes... Is it worth less now...yes it is to be honest. If the car was not correct then the decision to protect my own A$$ would have been a lot easier...

Just my thoughs ... Lots of luck

Bob

[QUOTE=RHeyboer]I am in the middle of purchasing a 68 with a 427/390 big block, where do I check to make sure this is the original motor?
2nd question: how much should this be worth? the body needs paint[/QUOTE]

 Here's a tough one to figure out,,, I heard G.M used an 18 inch wheel to finish the deck on blocks, If your engine was rebuilt /overheated and decked blocked & restamped,,, the new machines use around a 8 to 10 inch cutter. Different sized arc's. Might need a microscope for this one. (Hope I x-plained rite). So is it really an original block or cut and restamped

huk_finn38834.4916666667

GM used a HUGE machine(a "broacher") to "scrape" the top & bottoms of the engines, producing what we now call "broach marks". It is basically the same as using a scraper to scrape something. The broach marks on the surface of the engines were straight, front to rear, and look like lines, well...scraped into the surface.
This machine(s) were the size of a large locomotive engine. Wanna see one? HOW'S THIS?
This is an actual photo, of one of the machines that GM used. Its not a really good pic, cause it is old, but I think you can get the idea. If you look closely on the right side of the pic, you will see a big-block going thru. The left side(of the pic) was for the bottom(crank) side of the block, and then the blocks were swapped, and sent down the other side.
Neat stuff, here!

Oh, yeah....some of the old-timers said that when this machine was running, it was like a small earthquake goin on! It shook the ground/floors something awfull!Adams' Apple38834.8244328704