Where is the engine stamped 2.4?

The engine block itself will have B5254T4 on the deck if it is an R block, B5244T5 if it is an S60 T5 block. (B = gasoline (benzin), 5 = cylinders, 2.4/2.5, 4 = valve count, T = yup, last number is series number for engine of that displacement)
Everything is the same except for the pistons, block bore, fuel injectors, and PCV can. (Hoses come out slightly differently) I have had two of the 2.4s and they came with two different intake manifolds, one was identical to the S60R manifold. The other merely did not have a certain boss drilled, no big deal.

 

I couldn't find the stamp you were referring to. It said "B3340 2.4" on the cylinder head and 1007671 Volvo Germany on a plate over the firewall

 

The 2.5 that comes with the R is knock for cracking cylinder liners in stock form. The 2.4 is commonly swapped in place of it as someone said earlier the pistons/bore are different. They are 81mm (2.4) pistons vs 83mm (2.5) allowing for thicker cylinder walls that can handle a substantial amount more power . It’s a difficult engine to find let alone already swapped into the car. You got lucky

 

Neat. So how does one find out if they have a 2.4 exactly since I can't locate the engine code anywhere?

 

It's stamped on the block

 

It's just hard to see and is usually oxidized up. Hit it with a wire brush and pb blaster.