I'm sorry for the dissapointing news. At the mileage you have on your vehicle, if you are seriously considering keeping the B28 alive, you would be well advised to replace the timing chains as well. The non-even firing cylinders are very taxing on the timing chains. I would not put the B27 or B28 into the same category of reliability as the rest of red-block engines or the B280.

If I was in your shoes, I would seriously consider swapping in a B230F from a 240 (the fuel injection is easier to swap than the 740), or upgrading your B28 to a B280 (which would require transplanting the fuel injection system as well). -or just getting a VERY reliable 4-cylinder equipped 240/740/940 of the '85-'95 vintage.

If you are serious about pulling the heads on your B28, you will need several special tools (which are not cheap, and best borrowed from your Volvo dealer). The timing chain sprockets must be held in place (and tension) while the head is removed. FYI, a set of timing chains will run about $750 for the chains/sprockets.

Sorry to hear about the engine issue.
Fitz Fitzgerald.
--
'87 Blue 240 Wagon, 255k miles.