Overdrive : SMR shortie or Gear Vendors?

At the MATS I bought a 3.91 ring and pinion to Cass ( DoctorDiff ) and now I would like to buy an overdrive. I saw 2 Gear Vendors models , one with a 18" Tailhousing and an other with a 8" Tailhousing. Can I put an 8" on an Ebody?
I saw that SMR sells a OD also, a shortie overdrive ( with the GV product ) without modify the cross member.
Can you tell me your feedback about these 2 products. modifications of tunnel, cross member, adjust pinion angle to the shortened driveshaft.
Thanks

Looking at their shorty tailshaft housing, I don't see the shifter rod bracket attach points. That might cause issues? Looks like the rear tranny mount location is the same. My experience is with a B-bdoy though, a '69 Charger Daytona. You may want to address this on the the Cuda-Challenger discussion board too...

http://www.cuda-challenger.com/