How to make a pulldown menu display custom meta terms in a theme?

Still not sure what exactly what you aiming for, but having come back to this question i wanted to at least try to offer a solution.

So try this out, and see if that’s the kind of thing you had in mind with the dropdown… ?

add_action( 'add_meta_boxes', 'add_inventory_metaboxes' );
function add_inventory_metaboxes() {
    add_meta_box('inventory_information', 'Inventory Information', 'inventory_information', 'inventory', 'side', 'default');
}

function inventory_dropdown_opts() {
    return array(
        'Option 1' => 1,
        'Option 2' => 2,
        'Option 3' => 3,
        'Option 4' => 4,
    );
}

function inventory_information() {
    global $post;

    $stk_num = get_post_meta( $post->ID, '_dappcf_i_stocknum', true );
    $vin_num = get_post_meta( $post->ID, '_dappcf_i_vin', true );
    $drp_dwn = get_post_meta( $post->ID, '_dappcf_i_dropdown', true );
    if( empty( $drp_dwn ) )
        $drp_dwn = 0;

    wp_nonce_field( 'inventory_nonce', 'inventorymeta_noncename' );
    ?>
    <p>
        <label>Stock #</label> 
        <input type="text" name="_dappcf_i_stocknum" value="<?php echo $stk_num; ?>" class="small-text" />
    </p>
    <p>
        <label>VIN</label> 
        <input type="text" name="_dappcf_i_vin" value="<?php echo $vin_num; ?>" class="widefat" /></p>
    <p>
        <label>Inventory class</label> 
        <select name="_dappcf_i_dropdown" class="widefat">
        <?php foreach( inventory_dropdown_opts() as $text => $value ) : ?>
            <option value="<?php echo $value; ?>"<?php selected( $value == $drp_dwn ); ?>><?php echo $text; ?></option>
        <?php endforeach; ?>
        </select>
    </p>
    <?php
}

add_action('save_post', 'txpbs_save_events_meta', 1, 2);

function txpbs_save_events_meta( $post_id, $post ) {
    if( 
        !wp_verify_nonce( $_POST['inventorymeta_noncename'], 'inventory_nonce' ) || 
        !current_user_can( 'edit_post', $post_id ) || 
        $post->post_type == 'revision'
        )
        return;

    foreach( array( '_dappcf_i_stocknum', '_dappcf_i_vin', '_dappcf_i_dropdown' ) as $field ) {
        if( isset( $_POST[$field] ) ) {
            if( '_dappcf_i_dropdown' == $field ) {
                if( in_array( $_POST[$field], inventory_dropdown_opts() ) )
                    update_post_meta( $post_id, $field, $_POST[$field] );
                continue;
            }
            update_post_meta( $post_id, $field, $_POST[$field] );
            continue;
        }
        delete_post_meta( $post_id, $key );
    }
}

Follow-up #1
If you need to show the dropdown in the front end, just do it the same way i did inside the inventory_information function, like so..

    <select name="add-a-name-here" class="widefat">
    <?php foreach( inventory_dropdown_opts() as $text => $value ) : ?>
        <option value="<?php echo $value; ?>"><?php echo $text; ?></option>
    <?php endforeach; ?>
    </select>

Your dropdown options are defined in the inventory_dropdown_opts function, so you can use the same both front and admin side, and see the same data.