Having had a '68 144 which I converted from a B18/auto to a B20 M410, find the addition of the OD is the only way to go for a 140. I never saw a 144 come with an M41 OD, but maybe a few later '73-74 did.
I think the main diff from the early '67-69 models that should be considered is that the front end was weaker, smaller lower a-arms, ball joints, wheel bearings, tie rods etc. Anything after '70 is better. For the same reason any 240 after '83 is better. Taking it a bit further, any 140 from '73 on shares a lot with the 240, so a 240 is quite refined over the years, and many bugs worked out that made the early 140 pretty basic and raw by comparison. My choice would be a '71-72 142E if I was to look again.
I have both a '73 144 and '91 245 and the double wishbone A-arm on the 140 is a much stronger design, tighter handling, although some would say the geometry suffers when pushed. I thouroughly enjoy the handling of the 140 over a lot of other cars, not just Volvo's.
As far as performance, most vintage enthusiasts will agree, a n/a B20 flows much better than any later motor found in a 240 n/a. The only upside to a 240 is the potential to add a turbo at little cost or effort or just get one with a turbo.
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'89 245 sportwagon, destroyed by hit & run driver, RIP. '04 V70 2.5 T Sportwagon, 12k mi and '91 245 5-speed, 209k mi, replaced the '89