create metaboxes.php

<?php

// Do this so that the chapel_get_client_options WP_Query/get_posts ONLY happens
// when the field is run (otherwise this query will run on EVERY wordpress page-load,
// whether page has CMB2 fields or not)
public function chapel_get_client_options_cb() {
	return chapel_get_client_options( array( 'post_type' => ' clients ', 'numberposts' => -1 , 'orderby' => 'name', 'order' => 'ASC' ) );
}

function chapel_project_metaboxes()  {
	// underscore hides meta box from custom field list
	$prefix = '_chapel_';

	// YOUR_TEXTDOMAIN == This should be something unique to this build.. like 'chapel'

	$cmb = new_cmb2_box( array(
		'id'           => 'project_metabox',
		'title'        => __( 'Project Overview', 'YOUR_TEXTDOMAIN' ),
		'object_types' => array( 'project' ),
	) ):

	$cmb->add_field( array(
		'name'    => __( 'Client' ,'YOUR_TEXTDOMAIN' ),
		'id'      => $prefix . 'project_client',
		'type'    => 'select',
		// Do this so that the chapel_get_client_options WP_Query/get_posts ONLY happens
		// when the field is run (otherwise this query will run on EVERY wordpress page-load,
		// whether page has CMB2 fields or not)
		'options_cb' => 'chapel_get_client_options_cb',
	) );

	$cmb->add_field( array(
		'name' => __( 'PO Number', 'YOUR_TEXTDOMAIN' ),
		'desc' => __( 'PO Numer for this job.', 'YOUR_TEXTDOMAIN' ),
		'id'   => $prefix . 'projectpo',
		'type' => 'text_medium'
	) );

	$cmb->add_field( array(
		'name'    => __( 'Project Staus', 'YOUR_TEXTDOMAIN' ),
		'desc'    => __( 'Status of this project.' ,'YOUR_TEXTDOMAIN' ),
		'id'      => $prefix . 'projectstaus',
		'type'    => 'radio',
		'options' => array(
			'estimate'  => __( 'Estimate', 'YOUR_TEXTDOMAIN' ),
			'invoice'   => __( 'Invoice', 'YOUR_TEXTDOMAIN' ),
			'completed' => __( 'Completed', 'YOUR_TEXTDOMAIN' ),
		)
	) );

	$cmb->add_field( array(
		'name' => __( 'Project Number', 'YOUR_TEXTDOMAIN' ),
		'desc' => __( 'Project Numer for this job.', 'YOUR_TEXTDOMAIN' ),
		'id'   => $prefix . 'projectnumber',
		'type' => 'text_medium'
	) );

	$cmb->add_field( array(
		'name' => __( 'Due date.', 'YOUR_TEXTDOMAIN' ),
		'desc' => __( 'Date project is due.', 'YOUR_TEXTDOMAIN' ),
		'id'   => $prefix . 'projectdue',
		'type' => 'text_datetime_timestamp',
	) );

	$cmb->add_field( array(
		'name' => __( 'Date Completed', 'YOUR_TEXTDOMAIN' ),
		'desc' => __( 'Date project completed.', 'YOUR_TEXTDOMAIN' ),
		'id'   => $prefix . 'projectcompleted',
		'type' => 'text_datetime_timestamp',
	) );

	$cmb->add_field( array(
		'name' => __( 'Invoiced' , 'YOUR_TEXTDOMAIN' ),
		'desc' => __( 'Has this poject been invoiced?' ,'YOUR_TEXTDOMAIN' ),
		'id'   => $prefix .'projectinvoiced',
		'type' =>'checkbox',
	) );
}
add_filter( 'cmb2_init', 'chapel_project_metaboxes' );

plugin.php

<?php
function chapel_add_edit_form_to_frontend( $content ) {
	if ( isset( $_GET['edit'] ) ) {
		if ( current_user_can( 'edit_posts' ) && wp_verify_nonce( $_GET['edit'], 'edit' ) ) {
			$content = cmb2_get_metabox_form( 'project_metabox', get_the_ID() );
		} else {
			$content = '<h2 class="edit-error">You do not have permission to edit this post.</h2>';
		}
	}

	return $content;
}
add_filter( 'the_content', 'chapel_add_edit_form_to_frontend' );

/**
 * Modify the edit links to point to the front-end editor.
 */
function chapel_modify_edit_link( $link ) {
	if ( ! is_admin() ) {
		$link = esc_url_raw( wp_nonce_url( remove_query_arg( 'edit' ), 'edit', 'edit' ) );
	}
	return $link;
}
add_filter( 'get_edit_post_link', 'chapel_modify_edit_link' );

/**
 * Hook in later and prepend our title/content fields to our existing metabox
 */
function chapel_edit_core_fields() {
	if ( ! is_admin() ) { // only if on front-end

		// Get existing metabox
		$cmb = cmb2_get_metabox( 'project_metabox' );

		// and prepend title
		$cmb->add_field( array(
			'name'   => __( 'Title', 'cmb2' ),
			'id'     => 'post_title',
			'type'   => 'text',
			'before' => 'chapel_edit_core_maybe_redirect',
		), 1 );

		// and content fields
		$cmb->add_field( array(
			'name'  => __( 'Content', 'cmb2' ),
			'id'    => 'post_content',
			'type'  => 'wysiwyg',
		), 2 );
	}
}
add_action( 'cmb2_init', 'chapel_edit_core_fields', 99 );

/**
 * If edit was saved, redirect to non-edit page
 */
function chapel_edit_core_maybe_redirect() {
	if ( isset( $_POST['post_content'] ) ) {
		$url = esc_url_raw( remove_query_arg( 'edit' ) );
		echo "<script type='text/javascript'>window.location.href = '$url';</script>";
	}
}

/**
 * We don't want CMB2 to fetch data from meta for post title and post content
 */
function chapel_cmb2_override_core_field_get( $val, $object_id, $a, $field ) {
	global $post;

	if ( in_array( $field->id(), array( 'post_title', 'post_content' ), true ) ) {
		if ( isset( $post->ID ) ) {
			$val = get_post_field( $field->id(), $post );
		} else {
			$val = '';
		}
	}

	return $val;
}
add_filter( 'cmb2_override_meta_value', 'chapel_cmb2_override_core_field_get', 10, 4 );

/**
 * We don't want CMB2 to save data to meta for post title and post content
 */
function chapel_cmb2_override_core_field_set( $status, $a, $args, $field ) {
	global $post;

	if ( in_array( $field->id(), array( 'post_title', 'post_content' ), true ) ) {
		if ( isset( $post->ID ) ) {
			$status = wp_update_post( array(
				$field->id() => $a['value'],
				'ID' => $post->ID,
			) );

		} else {
			$status = false;
		}
	}

	return $status;
}
add_filter( 'cmb2_override_meta_save', 'chapel_cmb2_override_core_field_set', 10, 4 );