The 1st question should be, is the frame under your truck the original frame for the 50s truck, or is it a more modern frame? Lots of these trucks have been updated with Dakota frames, or have had the original frame modified with an independent front suspension. With out knowing what frame is under your truck, figuring out which trans cross member it could use it a guess at best.

What year the Dakota trans cross member is in the truck right now is also going to make a difference. I believe the 93 model year Dakota trans mounts are no longer available (it was a 1 year only piece), so if the current trans cross member was out of a 93 Dakota, it had to be modified to either install the older, or the newer trans mount, or what ever mount was used for the 727. Farther more, if the Dakota trans cross member as from a 90 and newer, it probably was set up for the 500 or the 518 trans already, someone modified it to use with the 727.

At any rate, the trans cross member will need to be moved towards the rear about 4" for the 518 to fit where a 727 resides.(you will need to compare where the trans mounts bolts to the trans compared to how far behind the bell the trans mount bolt pad is located, its been a while and I don't remember the exact differences in length). Then its just a matter of modifying the cross member so what ever trans rubber mount you use will work. Gene