67 cuda 340 engine swap - thoughts

I have installed a 1973 340 block (stroked to a 416) in my 68. I did what you are talking about- used my 318 timing cover, used my 68 318 balancer and installed the bolt on pointer. You can find those on ebay all the time. It is easier than trying to find a cover with the cast in markers. The bolt on pointer is a thin piece of metal that bolts on the two lower bolts of the timing cover. I used the 68 waterpump (can buy new for a reasonable price). The driver side outlet would cover the cast in marker on the later cover.

Swap your cover on the 273 and get a new 67-68 water pump and you will be set.