1st thing you need to do is bump compression....Look for a set of heads no bigger than 180cc runners and 64cc chamber...this will be a good start....

Or a cam swap.... but too big and you'll have to "chip" The ECM...

I am doing the same swap...But into a 89 Astro Van...I am tearing it down ( crate motor) and putting in flat tops or so and decking the block.....with reverse rotation water cooling you should be able to handle 10:1 easy....(91oct)