Porsche was not sloppy with engine numbers on production cars. If it was a 1974, it came with a 1974 engine. You can verify the original engine number with a COA. Note that the 1974 2.7-liter North American engines were much better than the 1975 versions as they didn't have the thermal reactors. And yes, a replacement engine typically hurts the value.

Hurts the value some, but it's not like 74s are a hot collector item, unless they're quasi zero mileage museum pieces.

I'd use that to bring down the price maybe, but I wouldn't pass on the car if it's otherwise very nice.

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Only the CA cars came with thermal reactors in 75. Other 49 states got the two heat exchangers flowing into single entry, single exit muffler.

I'd agree with Rick on value.

Maybe the first owner money shifted it way back in 75 and here you are.

You are half right.

A 1974 Targa engine does not start with a 614-, it starts with a 634-. A 911S Coupe and a 911S Targa from 1974 all start with a 634, not a 614. A 614 is for a regular 911 and regular 911 Targa.

A 1975 Targa S and a 1975 Targa Couple start with a 645- if they are US Cars. If they are not US cars, they would be marked with a 635-.

So the car you are looking at does have a 1975 engine from a 911S USA Coupe or Targa if it has a 645-. If the chassis is a 1974 it should have a 634-.

What month and year was the car made? If the matching is important to you, you may want to look at another car. If not, it would be money off. Probably around $4K.

Another thing.

You have a regular 1974 911 Targa, not a 911 S Targa.

A 1974 Targa (Regular) would be : 91141XXXXX
A 1974 S Targa (S) would be : 91143XXXXX

So if its a '41' its a regular, and if its a '43' it's a S.

Looks like you have a regular 911 Targa with 1975 911 engine.

PS. All these numbers are in the Porsche 911 RedBook and taken from the latest edition (2015)