Easiest giveaway is a fuel pump boss- probably has a blockoff plate bolted on it now. Magnum timing covers had no provision whatsoever for a mechanical fuel pump.
Just the fact that you have v-belts means you have an LA cover, since v-belts necessitate a standard rotation water pump, and a magnum timing cover generally requires a reverse rotation pump- thus needing a serpentine drive.
And no, the LA pumps do not fit on a magnum timing cover, so that eliminates that possibility.
When you pull off your harmonic balancer, you will most likely see one of the following two timing covers- the one on the top has seal installation from the inside, the one on the bottom installs from the outside.
View attachment 1716016511
View attachment 1716016512
My guess is you'll find the one on the bottom, since that is the style that is still available new and would probably be the one sourced by a crate engine builder.
Below is a pic of a Magnum timing cover, just for ***** & grins. You can see the differences.
View attachment 1716016513