Found a V20 with no power but I have questions......

[tsubaki]

That one looks like a 25'' transom (can't tell).
You will probably have to do some transom work to make them fit.
If you do decide on twins, think about a bracket.
I know the "75's were rated for twin 115's, but I'd be more concerned with the weight.
From what I remember, there was a couple of V's that had twin 75's on them and the owners said they would do around 30 mph.
That would be a great project either way you decide.