There are several types of mounting kits out there. Probably the easiest type to use would be the ones made out of round tubing, with mounting plates which bolt to the inside of the framerails. Chevy Duty and I'm sure several others offer this kit. In fact, if you have a local "speed and performance" shop, you could likely get one there. It would be called a "universal street rod engine mounting kit."
I thought there was a blurb in the Tech Tips section here awhile ago which detailed some of the issues of performing the V-8 to AD swap, couldn't seem to find it earlier today. However, there was an article written up for Hot Rod or Rod and Custom back in the seventies called "V-8 Juice For Your Stovebolt" which detailed this exact swap. It's floating about in a few places on the 'Net. You might want to check out the technical section at:
www.chevytrucks.org Hope all goes well with your project! Keep us posted.
Regards,
Wannabe
