I've got a friend who wants to put an overdrive trans in his 76 d100 with the small trans tunnel. He looked into the gear venders unit but didn't like the price. So now he wants to go with an a518 factory overdrive n was wondering what mods need to be done to the tunnel and mount area do this swap. Any help would be great.

not sure about the floor hump wether it needs to be the small or big for the A518, but I do know that need to find a 88-93 truck that came with the Auto OD's to use there cross member or if he can't find one then maybe customize a cross member cause I believe they use a totally different mount than the standard 3spd autos did.

I put a 518 in my 77 CrewCab & I can promise you dealing with a reg trans tunnel will be harder to do than mine was.
I cut everything that was extra off the outside of the case to help make it fit the only saving grace was the long floor was able to be jacked up to clear
I getting ready to put a 93 firewall & floor with trans tunnel in it

Use the crossmember for the 518 in a 90-93 so the driveshaft angle stays correct

I'll see if I can find the pics of everything that was cut off & hammered to fit the early A/T trans tunnel

Thanks for the info guys! This should get him on the right track.

Check out PATC trans site. They have everything you need.