I originally posted this at Steve's Nova Site, but since it's not the original engine, and apparently a truck engine to boot, I couldn't get much help. Here's the info I have:

It's in a '63 Nova SS and the guy I bought it from told me it's a 250, so obviously not original. Here's the code and serial from the pad behind the distributor:

F0524TAC
C4F455981

Block ID is 348675

I think it's a 250 from a '74 truck, but all the web sites I can find only list V8 codes, so TAC doesn't turn up anywhere. I'm pretty sure the F0524 means it was cast in Flint on May 24th and the T makes it the GM Truck Division. Three letters should make it post '70, but the serial doesn't seem to be formatted properly. At least according to the way V8 serials are supposed to be formatted. Do 6's have a different format? My guess is that the first 4 makes it '74 and the C and/or F confirm Flint.

I'm hoping someone here has a good truck book and can look this up for me. In the mean time I'm off to the library to see what they have on the shelf there to help with this.

I'd really appreciate any help y'all can give me.

Hi Scott.
The 348675 number indicates that it is a truck 250 built between '62-'79. Nothing new here. You are correct that it was built in Flint on 5/24. Usually the next digit after that indicates the year but you have the TAC code which I can't seem to find in any of my sources.

Thanks for trying. I went to the library today and was very pleased to find they had Motor Truck Manuals covering about '60 through '85. My '68 Motor Manual lists engine codes or all the passenger cars from 62-68, so I figured I was in once I saw all the Motor Truck Manuals. Nope. For some reason they don't list the engine codes in the truck manuals like they do in the auto manuals. Unless I just missed 'em somehow. I got there about 20 minutes before they closed, so I didn't have much time to look since I promised my daughter I'd help her pick out two books to check out. I'll probably go back on Tuesday unless someone here has the magical book that lists them. I didn't get a chance to check the Chiltons and various other books they had there.

You know I've been amazed by the collective knowledge of the members here. I'm sure someone has the information you need. Good luck.

I have a book for the Blazer/Jimmy that has engine codes.
The T means it's a Truck, the AC means it's a 73 or 74 250.
It looks like they used the same code for both years.
The AC also identifies the transmission but my book doesn't show that.

Biff

My Hollander list at least 10 different applications from 1970 to 1980 for a TAC engine. All are 250 and from trucks.