If your considering converting a normally aspirated engine to turbo power, the engine block assembly from a B21A or B23A carburetor motor is a good choice as it already features lower compression pistons.
(The carby piston crown has a recess to give a lower static compression ratio - a B21E/F piston is flat and a B21 ET/FT has a 21cc recess).
Fuel injection is best, so try and source a K-Jet FI cylinder head with provision for mechanical injectors.
One essential addition is a turbo oil drain (turbocharger back to sump). For a B21/23 240 block, you can fit an oil return line into the larger 'bell shaped' sump from say an 80-on model without removing the engine (only raising). If the engine is dissasembled, an option is to drill a large hole through the block and insert an oil return tube. Oil pressure to the turbo is obtained by fitting a tee fitting into the block sharing with the standard oil pressure switch. Source a B21ET/FT exhaust manifold and igntion distributor (boost retard feature) from a dismantler.

Return Line Sump Modification: Due to Volvo engine's approx 15 deg angle tilt, a turbo oil drain entry point 'into' the Volvo sump needs to be positioned as high up as possible to avoid having to pump through a sump fluid layer. After oil exits the turbo bearings it resembles a wipped froth and needs an unrestricted flow into the sump, otherwise there could be a pressure build-up & the turbo bearings will destroy themselves as new oil won't be pumped thru properly.

Position the hole where a B21/23ET/FT return pipe would drain in. Approximately half inch inside diameter pipe should be used, with attachment to steel sump by brazing or silver soldering as you can't weld all the way round with a stick. Use oil resistant rubber or silicon hose to connect up the turbocharger oil return line.