Drag Radials on a 67 barracuda notchback

Hey everyone, here is my question. I have a 67 barracuda notchback, stock wheel tubs in the back. It currently has 15x7 cop rims with 245/60/R15 on them. I picked up another 2 cop rims to put some drag radials on as it really needs them the next time I go to the track...wheels spun like crazy with the radial t/a's and thats with a sure-grip! Has anyone had experience doing this and what is the biggest size tire you think I can fit on it using the stock wheel wells in the rear? the 245's fill it up pretty good but there is some room for more.... Any suggestions? and any preference as to what brand drag radial I should get? I've never bought any before but I hear good things about the M/T ET Streets. And also The Nitto drag radials. Thanks for any info.