If so any idea what year the castings that had both the LA and the magnum bosses started?
Is there is a specific task you want to accomplish or just wondering about the info itself?
The 1991 Dakota 318 appears to be a test run for some of the Magnum features. It had a water pump and serpentine belt drive similar to the Magnums but not the same, as well as the engine mounts
@DionR mentioned. I never looked at the engine mounts on these, and I have only ever seen two of these. The 1991 v6 Dakota was still LA based and used v-belts.
In 1992 the Magnum 318 was available but the 360 was still LA based. The 1992 pickup truck LA 360 that I recently pulled does not have the Magnum engine mount bracket mounting bosses cast into the block. I will try to remember to check the casting date on it tonight.
In 1993 the 360 was now also a Magnum but the pickup trucks were still the old body style. There is a chance some LA engines were still produced in 1993 but I have never seen one yet. I have a 1993 D250 old body style with 360 Magnum and it uses LA engine mount brackets. I am trying to find the pictures I took when this came up before, but I think it has the Magnum bosses cast into the block and they are not drilled and tapped with threads.
Once the new body style trucks came out for 1994 model year the blocks all had the newer Magnum mounts to fit those trucks but still retained the older LA mounting ears. If I am not mistaken, some trucks or vans even had a bracket to support the transmission lines bolted to one of the LA mounting ears.
Finally, the race R blocks changed several times and I am not sure of all the details and part numbers, but some had both LA and Magnum mounting ears and bosses.
I hope I did not screw up those details too bad.