I saw those engines on eBay (assuming that's what you got).

It's become a fairly well trodden path to put an OHC motor in an earlier car.

First, you need to decide if you are going to stand it up or keep it laid over. You can do either. You need to fabricate front motor mounts either way, but if you stand it up, you can bolt the existing transmission right up to the new motor, and not have to worry about anything from the flywheel back. To stand one up, you just need to use a B20 oil pan, oil pump, and (I think) oil tube (from pump to block). On a 140, I think you might have some interference with the intake manifold and the brake booster when stood up, I think some models of the intake have better clearance, or you can replace the brake booseter with a more compact model from the 1800E/ES.

If keeping it laid over, you'd probably have the easiest time just getting a later model transmission and bellhousing to match the motor - M45/46/47. (4 spd, 4 spd+OD, 5 spd). Those bellhousings have 'twisted' bolt patterns between the engine and trans, but you can't bolt an M40/41 to them.

All in all you will have changed valve adjustments every 5 - 10K miles for timing belt adjustments every 70 - 80K miles. A stock B21 motor won't be much of an increase in power or refinement over a B20 in good shape (a little less valve tapping, I guess). Typically people put B21/23 Turbo motors into older cars to get a *big* jump in power.
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I'm JohnMc, and I approved this message.