I think a read somewhere, possibly this board, that they were used in military equpiment or 4x4, not sure on the the truth of that. I have a .jpg of the homolagtion papers if you want to see them.

Captain Bondo from the Turbobricks forum has put up a bunch of scanned images from Volvo's R-Sport catalogue for 140 engines, it's a half interesting read.
Best part of the Volvo Solek layout was the sounftmounts. Both of the Swedish head suppliers appear to have copied the Volvo Competition combustion chamber, which isn't the greatest IMHO.

A cylinder head is the most important part of a good motor, most of mine feature standard vavles. The rest depends on how powerful you want to make the motor. My street motor with SU's has a hi lift D on the intake (.300" at lobe) combined with a D profile on the exhausts & is great for SU or Injected motors. Valve spring wise you just need 4 dual spring for the intakes. After that stuff just gets bigger & bigger & more dollars.