12 string lap steel string spacing and scale length question

[Ferdinand van den Berg]

Hi,

I have a very nice commission to make a 12-string non-pedal lap steel. It will be like a 12-string guitar, with string pairs to get a chorus sound

We are in doubt about a suitable scale length and string spacing, between the two strings within the pair and between the string pairs.
Any suggestions, or measurements from your favorite 12-string lap steel would be most appreciated.
Also suitable tunings would be appreciated.

Thank you so much!
Ferdinand van den Berg
Fern's Guitars
Amsterdam