Unless there is excessive wear in the link's pin holes,  the link should force/pull down on the breechblock(BB) to"drop back down" to its final position as it goes 'over center" in its travel, assuming the lever is able to be fully closed, even tho there may be slight interference fit of BB to barrel face at the fully closed position or the interference fit  of a long seated bullet in the throat as one closed. . 
My suggestion is to have a 3-4 thousandths clearance
between BB and barrel face when action is fully closed.
beltfed/arnie

I'm working with a new Wyoming Armory/MVA highwall action. I measured the amount of play in the linkage/block travel and its about 0.015". At least this is the amount of play in the breech block after the lever is closed up against the tang. There does not appear to any excessive clearance between the link pins and the block and lever. I guess it just adds up and maybe this amount is not really considered "excessive"?

I like the idea of minimal block-to-barrel clearance, maybe .001-.002". Anymore than this and I would think you would have to then consider how deep to make the rim recess depth. If you wanted more barrel-block clearance then one might have to consider maybe making the rim recess depth shallower where the case-head remains a little broud of the end of the barrel to minimize head-space issues. What is customary to do here?

If you load with the bullet into the rifling a bit, and the block then tends to cam the cartridge in, this will help keep head-space to zero or a minimum.

Maybe I don't understand, but block to barrel clearance is not critical within reason. If you have .012" clearance between the block and barrel and the barrel is chambered so the cartridge rim projects .010", then you have .002" headspace clearance. Conversely, if the block and barrel is tight and the barrel is chambered deeply, then you have unknown headspace clearance.

That said, I like the block to barrel clearance to be snug and just slightly tighter on a cartridge. The over center drop of a hi-wall block would add less than .001" to the headspace clearance.
Chuck

Hey everyone, sorry this got confusing but I was not suggesting that there was an issue with excessive clearance developing between the end of the barrel and the breech block when the breech block goes over center and drops down upon closing the lever (although this is interesting). I was originally asking what the best practice should be for this fit up, either to include some clearance here or to produce an interference fit, between the barrel and block. I also mentioned that, because there is some play in my lever-to-block linkage of 0.015", that the block may not drop down by this amount if there is an interference condition say due to no clearance or when camming in a cartridge. The discussion went on to include how the rim recess depth should vary, with regards to the barrel-to-block clearance, to maintain a small head-space condition.