MK32713

I have a 69 428 stroker/455 crank Dport heads, 4 speed m-21....in a 67 firerbird convertible...its a ground up restoration ...just cant get it to run cool...always 220 or higher especially if I step in it...I have a 4 core alum rad...elec fans...checked the water pump..timing etc...any suggestions...im told maybe a block restriction?....giving up hope...lol...may just bite the bullet and drop an LS.....anybody have any ideas....