do not know that much about 740's, but what caught my eye was the OD.
In the 240 series, from 87 on the Manual Tranny was the M47 - true 5 Speed and the New Plastic single big headlights.

So I checked the Volvo Owners Manual link and found that indeed the 745 Turbo had indeed came with those dual square headlamps and

Manual transmission: fully synchronized five-speed with electrically operated overdrive

http://new.volvocars.com/ownersdocs/1988/1988_specs/88_740_turbo_wagon.html

so how come the 240's got the M47 which was then replaced by the M47II, which was to fix the bad points found in the first generation of the M47.

Did they know that the M47 couldn't handle it and so stuck with the M46???

It looks like a decent deal if the East coast rust hasn't gotten hold. It is stated that the OD is shot but there is another unit ready for installation. I believe the original OD would have been the J-type which was a stouter unit fitted behind turbo engines in the 700's. Not that many out there compared to the older P-type. Both will fit, so which one is being supplied as the ready-to-install spare?

We all love our Volvos so don't take this as criticism, but the seller mentions "top rated in safety/crash tests"...

That was close to 30 years ago. There's a Youtube video out there with a clip from some British TV show about cars (don't think it was "Top Gear"), in which they do an offset frontal crash of a 740 wagon and some modern but tiny Renault sedan and the little Renault comes off much, much better. There was significant distortion of the Volvo's firewall and floorpan into the driver's area, with strong likelihood of leg injuries.

Not to knock Volvo's achievements of those earlier days, but time has marched on. So has Volvo's - and everyone's - crash safety engineering.
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Bob: Son's XC70, my 83 244DL, 89 745 (Chev LT-1 V8), 98 S90 (recently sold) and 2010 XC60. Also '77 MGB and four old motorcycles