Counter rotation blocks require some machining at the rear seal area, yes some are compatible with hyd lifters but the true center oiler on the earily blocks will require a mech. cam and the blocks that will work in a hydraulic cam conf. require a plug or a limiter in the
oil journals that feed the lifters and a camer block has extra
oil return journal to the valley. You are right when it comes to a center oiler being a good block to use for our application but I have learned from the past - the better the lubrication one has the longer they live.
If you can find a Lemans block it will have the best oiling journals and a higher content of steel in the casting. They are out there - just takes time to find them.
hope this helps