PTC makes very good convertors and can loosen yours up if you think it is too tight. I went from a 9.5 in convertor to a 8 in when I had a 360/380 magnum crate motor in my D-50 and it picked up over 3 tenths in the 1/8.

8087406-CIMG0081.JPG (41 downloads)
1.33 60 ft,6.21 at 110.59 in the 1/8, pump gas small block,2950lbs,drag radials,mufflers and driven to track ...