I highly doubt it. Everything else about that car besides the engine change to something not even available in '85, based on the pictures we've seen, shows it to be a 442. To make sure, I'd check to see if it still had the trunk spid and match the VIN to the spid and check for RPO W42 on the spid. If the transmission is still original to the car, it should show OZ on the trans tag and the VIN derivative on the casing.
85 Arlington-built Cutlasses without body tags seems to be the norm. When I bought the gray 87 442 brand new, it had a tag. WTF? So I called a number my dad had for the production supervisor's office in Arlington. When we discussed it, he said that there was no requirement for the tag and if they had them, they put them on, but if they weren't supplied, they didn't put them on. (That's also when I found out they just trashed the records after the model year, so they had no information on my 85 there at the plant, and I'd have to go through GM/Oldsmobile Corporate. My dad said Corvette plant did that, too.). They figured with the introduction of the SPID stickers, the tag was not a big deal anymore. And that went for all the G-bodies built in Arlington, including the Monte SS as well. The holes are pierced for the screws, but nothing was ever put there. If the screw holes appear to never have had been used, it's absolutely normal. Pontiac plant used them and Lansing did, but in 1985, Arlington did not. And I have heard of some late 84 cars not having the tags, but I haven't actually seen an 84 without a tag. I don't know when that "tagless" situation started.
If you can get the gunk/dirt off, check the block casting numbers on top of the block behind the timing cover next to the oil fill tube. If it has casting 557752, it's a late 70s 350. It's not necessarily out of a 79
H/O, but they used the same engine with 3A heads. Everything about the 79 350 will pretty much match up and fit where the 307 stuff was, so swapping to the 307 HEI and carb and CCC stuff is a natural fit.
If it's a 556607, it's a 307. But I doubt that with the 3A heads.