Decode is from the 1985-1987 GM Light Truck parts books.
Truck VIN:1GCHK34W3FS117369
1= USA build
G= GM
C=Chevrolet
H=9,001-10,000lb brakes & suspension
K=Reg cab 4WD
3=30 series (1-ton)
4=2 door cab
W=LE8 7.4L 4bbl V8
3=checksum digit
F=1985
S=St Louis
117369 is the production sequence number
Engine VIN:CFS117369
C= Chevrolet
FS117369 Matches last 8 of vehicle VIN.
The three letter 1985 7.4L engine suffix codes will not tell you any more than the VIN. I looked up the ones listed in the parts books. All you can find out is they were the LE8 RPO in a 3/4 or 1-ton chassis trucks... VIN W... The alphanumeric prefix to the three letter engine code would be the build date... again not terribly informative.
Transmission ID code:N5P24
N=4 Speed Muncie CH465
5=1985
P=September
24=24th day of month
Some observations. Take them for what they're worth.
It looks like the numbers match your truck with some oddities.
- The stamped numbers on the engine don't look like GM factory stamps. The 1s have feet, the top loop of the 3 is not rounded, the upright on the 7 has a jog at the bottom, and the rounds on the 9 & 6 are oddly formed straight lines not circles. They also look like shorter and narrower characters than the stamps on the transmission. The GM stamps I've seen are usually block characters with rounded numbers like the ones on your transmission. The casting number would possibly clear this up or it might muddy the waters.
- The transmission is a 1985 4 speed truck transmission but the build date is September 24th. September 24th would normally be into the next production year... My 2005 K2500 was built in September of 2004. I'm not sure where the cutoff was in 1985. A build sheet from GM would tell the production month and year. If the truck was built prior to the transmission stamp date then the transmission was changed at some time in its' life. Not shocking on a full ton 4wd work truck.
The 1985-1991 hydraulic clutch setup isn't the easiest thing in the world to retrofit.
Look on the LH frame rail next to the bellhousing. If this was originally an automatic truck it'll probably still have the sheet metal retainer for the shift linkage pivot ball riveted on the frame.
Not sure any of this matters that much on a 1985 K30. I'm also not sure why someone would go to the trouble of re-stamping the engine pad in a 1 ton truck unless it was possibly done as a dealership re-power at some time or it was a hot engine or a machine shop that decked the block actually re-stamped it...?
Get the build sheet. I'm interested in what the story might be.