the 134 gas isn't as efficient as the r12 so it doens't cool as much

then there are different gasses which don't work so well when they are cold (working with fridge vehicles tends to show up loads of issues)

as far as the rad is conserned, there are several fixing points in the chassis so i'm sure you can trial fit the orignal, or, if that doens't fit, you can check out various different other rads

don't use the granada one, it will sit way too high/low as the mounts are in a different palce