Buy this and cut some more tread in them. Or at least you could find how much rubber until you hit the cords.
“ Tyre Cutter regroover HGV tread recutting regrooving tool. Ideal for HGV, Forklift or Race Slicks. Tyre Cutter. the one in pic is 240v. (The Rescut Mk3 will also run from a small inverter & 12v car battery has it's power consumption is only100 watts).www.ebay.co.uk
Maybe a bit more. but under 4K fitted surely?Guessing 460 / 70 r24 , about 500 a pop