Corvette rally wheels

[fast&low]

Ok guy's
Getting ready to install a CPP grand slam kit on my 69 SWB fleetside & I went with the 4/6 drop spindles/springs up front
I'm wanting to go with corvette rally's while my truck is under construction
I looked up old postings and learned that with a spindle drop I need to go with a 7 inch wheels up front so I was wondering what backspacing are y'all useing is it just an off the shelf wheel or do I need to ask for a specific backspacing?
Also what size tires are y'all running on these 15x7's
CPP grand slam kit consists of front wheel disc conversion and drop kit all-in-one
Part#6772GSK-5D
Thank you 4 looking