Swapping crankcases

["Slack Alice" Simon]

Good evening all

I have a late rubber mounted high frame crankcase.

I need,for a short while, an engine to fit a low frame car.

I assume the fore - and - aft positions of the relevant crankcases are the same - both having 4 speed gearboxes.

Do I need to raise the earlier 'case a bit, on spacers, to match the vertical positionof the later one?

If so, by how much?

Thanks

Simon