Wheel Backspacing

[mustrick]

I BOUGHT A SET OF MICKEY THOMSON ET STREETS THIS WEEKEND
AT THE OHIO FORD SUPER SWAP. THEY ARE SIZE 28X12.5. I WANT TO USE THEM ON MY 87 MUSTANG GT. I'M GOING TO ORDER 15X10
WHEELS FOR THEM BUT I DON'T KNOW WHAT BACK SPACING TO USE. DOES ANYONE KNOW FOR A FACT WHAT IT HAS TO BE?

87 GT, 393W, 10.7:1 COMP, 600 LIFT ROLLER, VICTOR JR HEADS
& INTAKE, REWORKED HOLLEY 750 DBL PUMP,90/10'S,MOROSO SPRINGS,SOUTHSIDE LIFT BARS,STOCK 8.8 WITH 4:30 GEAR,C-4 WITH 4000RPM GER STALL
RAN BEST OF 11.06@122MPH
WAS WOUND OUT TO FAR AT END OF TRACK, AND TRANNY SLIPPED A LITTLE BETWEEN SECOND &3RD
SO I HAD TRANNY REBUILT & BOUGHT 8.8 WITH 4:11'S, SPOOL, AND 33 SPLINE MOSER AXELS AT SUPER SWAP FOR $800
I ALSO HAVE A BIG SHOT NOS KIT THAT I'VE HAD FOR A YEAR BUT NEVER INSTALLED BECAUSE OF STOCK REAR END. I HOPE TO RUN HIGH 9'S WITH 150 SHOT OF JUICE. ANY ONE THINK IT'S POSSIBLE?