I too have a 327, that I just recently aquired. I have all the "Chevy by the Numbers" books, and still can't decode the suffix.
Block - 3858174 -C.4.6-
Pad - F 0309 AP
Any help would be appreciated.

mortec.com says 64-67 327 w/ two bolt mains

Yes, but I'm looking to decode the suffix AP.

AP does not exist, look again.

here is everything I have for a 66 cast small block. As indicated before AP does not exist.

1966 DI 283 air inj. react, m/t - 195 2 A
1966 DJ 283 Powerglide, A.I.R. - 195 - A
1966 DK 283 m/t, 4 spd, A.I.R. - 195 - Chevelle
1966 DL 283 A.I.R. - - 4 Chevelle
1966 DM 283 A.I.R., glide - - 4 Chevelle
1966 GS 283 4 spd, air cond. 195 2 full size/Camaro
1966 GT 283 A.I.R., glide 195 2 full size
1966 GW 283 - - 4 full size
1966 GX 283 A.I.R. 4 full size/Camaro
1966 GZ 283 A.I.R., glide - - 4 full size
1966 PS 283 a/c, 4 spd, A.I.R. 195 2 Chevy II
1966 PU 283 Pwrglide, a/c, EM 195 2 Chevy II
1966 QA 283 glide. A.I.R. a/c - - Chevy II
1966 QB 283 a/c - 4 Chevy II
1966 QC 283 A.I.R. - 4 Chevy II
1966 QE 283 glide, A.I.R., a/c - 4 Chevy II
1966 QF 283 A.I.R., a/c, 4 spd - 4 Chevy II
1966 WF 283 m/t, A.I.R. - 175 2 C-10, 15, 20
1966 WH 283 Powerglide, A.I.R. - 175 2 C-10 to 25
1966 EC 327 A.I.R., glide - 275 4 Chevelle/1200
1966 HD 327 a/c, spec high perf. 350 4 Vette
1966 HF 327 Powerglide, A.I.R. 275 4 full size
1966 HH 327 air inj. reactor 300 4 Vette
1966 ID 327 spec. high perf. - 4 full size
1966 KH 327 s h/p, A.I.R., a/c 350 4 Vette
1966 YC 327 m/t, A.I.R. 220 4 C-10 to 25
1966 YD 327 Powerglide,A.I.R. 220 4 C-10 to 25
1966 YH 327 hydramatic 220 4 C-30
1966 YR 327 Powerglide 220 4 C-10 to 25
1966 YS 327 m/t 220 4 C-10 to 35
1966 ZB 327 m/t, hi perf. A.I.R. - 300 4 Chevy II
1966 ZC 327 A.I.R., a/c - - - Chevy II
1966 ZD 327 Powerglide, A.I.R. 275 4 Chevy II
1966 ZG 327 A.I.R.spec hi perf. - 325 4 Chevy II
1966 ZH 327 sp hi per, EM, a/c - 325 4 Chevy II
1966 ZI 327 special high perf. - 325 4 Chevy II
1966 ZJ 327 spec high perf, a/c - 325 4 Chevy II

Triple checked. I't certainly is a AP. But I checked the box of parts that came with it, and I now believe it is not an automotive engine. The crank pulley is a montrously huge cast iron unit, unlike anything I have seen. And the 2 barrel intake has a governer on it. Must be some kind of industrial. Heads are 3876775 and match the block with a march 8th cast date. The pad stamp, is as clear as day, and actually looks like this
F 0309 2 AP. So I'm kinda wondering what the 2 means also.

It is also painted chartruse green.

You left out that 2 the first go around or else I would have know it was a marine engine. All marine engines are 3 digits codes with the first always a number 0-9, always.

Found it, a 1992 inboard/outboard Marine engine
(for a pleasure boat, ski, fishing etc)


2AP - 350-275 hp, no other info avaialble as to configurations

Thanks for the info. I need to keep digging as I don't see how a 3858174 327 block, that was cast in March of 1966, was stamped for a 1992 / 350.
I may be getting closer, as a couple of phone calls I made, point to the engine possibly coming out of a Massey Ferguson 510 combine. If so, I'm still trying to find out what horsepower it would be rated at. Thank you all for your help. :)

My info shows that block was also used for 350 engines

fwiw
Chevy did not start stamping 3 digit suffix codes until 1970 so I don't see how it can be before that. 1992 does seem out there though but that .

No telling what you have.

Can you post a photo of the 2AP stamp? Maybe seeing it with my own eyes can shead more info.

Sure Mike, here is a few pics. Thanks for your help.
1444

1445

1446

The code does not appear to resemble the ones Chevy engine plants used, the font and position appear different.

I think you have a bastard engine here and chances of finding anything about it are slim to none. It could be a remanufactured engine. Many of those on the market....

Back in 1968 I got a 1963 Impala SS (my dad's car) with a bad oil burning 283 and ordered a reman. from Sears to install in the car.

One more thing to check out.

Measure the length of the engine pad

late model block the pads are about 1-3/4" long
early engine use a pad about 3+" long
and 60 and 70's use a 4-1/2 " pad

I can't tell which it is.

It could be a remanufactured engine. Many of those on the market....
When I bought my trans from Coan, it had a number stamped on it for them to identify it for parts etc. Maybe someday,40 years from now, somebody will be puzzling over it trying to "decode" it!:D