Your method of using straight pins as measuring points should be very acurate (good idea). The Haynes manual calls for a difference of 3.0 +/- 1.5 mm. That's just a little over or under 1/8". I shoot for just a little over 1/16"of toe-in. You can also adjust camber by moving the struts at the top of the towers but this is much more dificult to set correctly. I've tried using a machinist level, framing square, and 360 degree magnetic base protactor but had little success. A small movement of the strut is several degrees. I actually had more success by watching tread wear (inside versus outside) and moving the struts accordingly. JC Witney sells a gauge that attaches to each wheel that should work well (check their web site for price). Castor can't be adjusted. jp

Just a note - on my 240 (your 740 may not be the same) I've found it's necessary to have different toe in on each side - to compensate for road camber.

Volvo's seem quite sensitive to this, and the outer tire wear seems to some extent to be a fact of life - obviously if it's excessive then adjustment is necessary, but using DIY methods it's only possible to measure the overall toe in.

Setting toe-in is simple, but you must achieve some sort of accuracy. To do that, lift the tire and chalk a band around it, and then spin the tire while having some hold a screwdriver blade against the chalked area. Brace the screwdriver on a jackstand or something. That will produce a line around the tire that is perpendicular to the axle. Now you can measure between the lines at the back and the front. The difference should be about 1/16 of an inch closer on the front. I also use the tire for the measurement IF the tire has a circumferential groove in it, which many do today.
After each adjustment roll the car back and forth at least five feet and steer ahead again to take the squirm out of the tire.
Centering the wheel if it is off after this is a matter of moving the tire rods an equal amount in the same direction, in other words extending the one towards the needed correction (if the wheel is steering left when going straight ahead, steer the left tire into the correction, which on a Volvo means lengthening that tie rod, and shortening the other by the same amount.
You can also pull the steering wheel and center that way.

Tire tread feathering such as you see is usually due to excessive toe...and based on your measurements that's what you have. A problem with your measurement method is that it's dependent on picking the exact centre of the tread on each tire. With the small measurements involved there's plenty of room for error.

But given the way you measured (if exactly on tread centre) you would have seen about 3mm if toe was on spec. You are well over that - too much toe.

To get my front end fairly close after a strut, ball jt, and tie rod job, I used two thin sticks, each about 4ft, overlapped so they would barely fit in between the front tire sidewalls from side to side, and held together with rubber bands. Extend (telescope) the stick assembly until each end touches a tire inner sidewall at the front of the tire, as high up as you can get them. Carefully remove the sticks without disturbing their combined length and get them around to the back of the tires and measure there - on the sidewall and again as high up as it will go. The gap you should now see (back width minus front) the toe. Volvo specify 2.5mm when measured at the sidewall.

My experience has been that 240's hold their alignments for a long time, so I've felt that the $50 or so for a good, professional alignment (independent tire shop) pays off in tire life and fuel economy.
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Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar 77 MGB, and a few old motorcycles)