I have found my block stamp behind the alternator bracket and can not find a site to decipher it. Would like to know if it was original before planning on a rebuild or swap. Was stamped as follows:

C 225 3 07 an iron cross stamp then an X

C: 1967 model year
225: Engine displacement
3 07: Engine built on 7 March 1967
Iron cross (called a Maltese cross) followed by X: All rod and/or main bearings 0.010" undersize when engine was built.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks Dan. I've enjoyed reading your posts, they have been very helpful on this site and others. According to my fender tag the car was built April 28th 1967. Would the time lines add up between block and fender tag? I've been debating a rebuild of the motor that's in it if original or rebuild of a complete 1980's slant six motor stamped 225 T4 24E. I also have a 68-71 complete motor stamped G 225 T 5 6 that someone suggested using the heads off of and the 80's cast block. Just looking to do minimal HP upgrades. Super Six set up, HEI, cam, shave the head or block which ever is best. We travel a lot to shows so gas mileage would be nice. A little rumble and power would be nice too.

Any opinions?

Sure, why not? It is possible the motor had to be shipped, or finished, or just sat around the factory for a month until it was stuck in your car. I really doubt any motor was finished on the same day it was installed in a vehicle.

Glad to help out.
Yes.
Assuming both engines are basically sound, I'd build the '67 engine. Not only is it original to the car, but it's got the nicer forged steel crankshaft with its larger bearings rather than the later cast iron item with smaller bearings. This is of no practical consequence except in extreme-duty service, but there is a certain warm fuzzy that goes with having premium parts in the engine. Also the '67 engine has solid valve lifters, which—though they will require periodic valve adjustments—means a much wider selection of camshaft options.
G: 1971 model year
225: Engine displacement
T 5 6: Built at Trenton Engine Plant on May 6, 1971

This would be a fine engine to build. Forged crank, solid lifters. Given the choice between this or the '80s engine, both basically sound, I'd pick the '71 engine.

Note if your car has an automatic transmission, you'd need an adaptor ring if you install an engine with a '68 or later crankshaft.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

I do have an automatic transmission in the car. Is there a date code stamped into that to see if it may be original as well?

Looks like I will pull that beauty this winter and bring her back to life and keep it as original as possible. Something nice about having a car that hasn't been molested.

I'll keep the spare '71 motor in case any major damage is found during the rebuild which has an automatic transmission already attached to it.

Looks like its to the For Sale ads for the '81 motor after I rob it of its distributor and fuel line set-up to start the fuel line modification for my car. It has 39,000 miles I'm sure someone can find a use for it.

When we get some clear weather here in Ohio I'll be sure to post some pictures.

Thanks for the opinions and help!