I wouldn't rely on the airbox cover, seems to me that yes only T5's had them, but not all T5's did. 850's had the turbo air box and the early s70's that you and I have Ray had them, but then Volvo stopped using them (as a cost saving measure?). 99 and up did not, based on all the pictures I've seen of engine bays on Ebay.

And as I am doing a little research sitting here, I've found that there ARE differences between B5234T and B5234T3.

850 T5:
B5204T - 210hp (300 Nm) (italian version for lower taxes)
B5234T - 225hp (300 Nm) (T5 as it is known in Europe)

850 R:
B5234T4 - 250hp (350 Nm)
B5234T5 - 240hp (300 Nm)

S/V70 T5:
B5234T3 - 240hp (330 Nm)

T has 15G turbo
T3 has 16T turbo

What I find very odd is that you would have an older engine in an S70.
Which leads me to believe you just have an old sticker. Look under your floormats for example, I bet they say 850.

Anyway - I'm pretty sure you have a T5.

DG
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1998 S70 T5M