OG Porsche 356 wheels + tyres

[nora]

At the moment my bus has 4x15 solid wheels fitted but I've been offered a genuine set of 4.5x15 Porsche 356 wheels and i'm wondering if they will fit correctly, will the offset be ok? If i was to get them what would be the best size of tyres to use. I might be being a bit cautious but are car tyres with a high loading going to be ok with insurance and police or are commercials the best way to go. I've done a search on tyres and theres a lot of conflicting advice out there. Cheers.