I just finished a 223/556 build using 74 parts, I used a wieger barrel from APEX a east german 74 trunnion I picked years ago, in fact the parts were all east german except for the bolt which is a 5.45 bulgy, yes the barrel needed to be trimmed to fit the rsb and trunnion and the gas block hole drilled, I have several 223 k-var bullet guides but others had no problem with using those guides with 223/556 so i kept the 5.45 guide, my only problem was not setting the rivets on the trigger guard real tight to the reciever, this cause a mis feed problem other than that I consider my rifle to be a workshop type model from eg74 to stg 941 as it would have been the natural progression in the workshops , using polish beryl mags
my wieger will be next in my shop just waiting on restorit to finish the wieger barrel unit
the wieger barrels are very accurate which should be expected from suhl. my wieger will use a 223 bolt bulgy and 223 bullet guide and wieger mags
I used a Henderson 80% with rails installed, I refuse to use ffl receivers in all my builds.
I have attempted to upload the pictures of this build which i posted in another thread on ak 223's here in february
you are a known builder and have alot of experience i think its easy to determine that it may be best to leave the 5.45 bullet guide and trim it if need be, but to answer your question yes the K-var bullet guide holes line up with the factory 5.45 guide holes in the trunnion