After quite a bit of Googling and forum-reading, I'm no closer to deciding which way to lash the valves... there is considerable disagreement on the subject, as usual. This is what I have read:

Obviously at TDC compression, both valves are as closed as they're going to get. It only requires turning the engine 90 degrees, eight times, and going to the next cylinder in the firing order to do both. But with really long opening/closing ramps, it's possible that a lifter could be a couple of thousandths "up".

The EO/IC also requires 90 degrees, eight times, and the use of a chart (or a good memory). The valves will absolutely be on the heel of the lobe though.

I have to lash my valves again anyway to determine if the .006"-tight when cold rule of thumb (Al heads, Fe block) is accurate, so that would be an opportunity to check if the two approaches read any differently, at least with my particular cam. Although it's 272@.050, it's a 1.00" mushroom lifter, so has a relatively fast opening and closing. From reading the cam card, the exhaust is a long way from opening at TDC (just leaving the seat at 95 ATDC) , and the intake has been closed for a while (seat = 99 BTDC). Even if that seat degrees are at .006" lift, no way are the ramps on a solid cam that long. I think.

Thoughts?