273 have a problem with a 1.88 valve. A bore notch is needed and is described in the engines book.
MtNemoMopar;
I re-read my post and edited the post with the "In bold" letters posted here to clear things up.
For a on the cheap improvement, (340 - 360 heads) it is OK, but if you have a few bucks to spend, spend on upping the anti on the 318 head or do a Magnum head swap.