Hey G508,
WRT resurfacing, when I rebuilt my last 270, I sent both my camshaft and lifters to these guys:
https://www.oregoncamshaft.com/At the time, I remember discussing the proper radius with them, and they seemed to be very knowledgeable wrt the proper dimensions and finish.
That was about 5 years and 2K - 3K miles ago. Engine still seems to be running OK with no issues.
At the time, I too was wondering about the hardness characteristics of the lifters. I was specifically concerned about whether or not there was some surface hardening on the lifter face, which might be compromised if they were ground.
The research I did at the time, indicated that they were made of "chilled iron". Research on that seemed to indicate that this process resulted in a fairly homogeneous part, indicating a consistent hardness throughout. Take that for what it's worth. That call is based on a couple of metallurgy classes taken over 40 years ago - so I'll certainly yield to anyone with more experience on that subject.
BTW, do you know what camshaft you have ? Is it the steel or cast iron one ?
As for new lifters, these guys have them. I didn't see a GM PN, but they do list the GMC series of inline 6s, including the 270, under the list of applications.
https://www.kanter.com/products/engine-valve-lifter-vl995I actually purchased a couple of these several weeks ago to evaluate for my current 270 project. They look OK, but I haven't had a chance yet to check them dimensionally.
I was also going to talk to the metalurgy prof. at the community college where I teach part time. Possibly check the hardness on these relative to one of the originals.
Best Regards...
