easy engine mounts

Well if those don't beat all! The slant 6 in the 67 Valiant has trans problems and I have a spare 318 waiting to go in so I have been planning to start the swap soon. I read somewhere else about doing the swap this way and I already have the truck mounts, cleaned and ready to go in.
I have several from a 80s Ramcharger and a 86 Ram truck, I have the thin biscuit and our local Mopar swap meet is this weekend, so I'll be able to find the other style biscuit.
My worry doing this has been the trans crossmember. I am using a 904 and the mount should be the same as the 904 from the slant6 Right?
If the trans mount is in the same place then the driveshaft lenght should work too.
I know ,I know, the brakes should be up graded and the 7 1/4 axle won't last long ,but this was a basic transportation daily driver up to Christmas. I don't plan on beating on it(I have a 72 Charger for that), I just want to try the swap out.