273 to 318 engine swap info please!!

Should be a bolt in swap except for maybe the electronic ignition. The 273 and 318 are both internal balance so no special flex-plate needed. If need be you can use the flex plate from the 273 on the 318 if the bolt holes in the 318 plate don't match. Hardest part of that swap is going to be the water pump. You will need a newer model radiator with the outlets on the bottom pass side to match the 318 pump. To change the pump to the old style you will need to change the whole timing gear cover so you will be able to see your timing marks.