Changed mine today. Not a big deal. TDC. Pushrods slackened off. Tank off. Rockers box covers off (hold down bolts very loose to start with but gaskets really wanted to hang on!!!). Remove etc etc
Now, the originals work OK, but are roughly finished (which doesn't effect operation obviously), but the arms are very heavy as are the hold down blocks!
The new arms are much lighter (see plan pic) as are the blocks.
I read somewhere that the oilways should be drilled out from the existing 2.5mm to 3mm. Well mine came as std as
2mm diagonally drilled hole with 'O' ring seal at the bottom so I compromised and went to 2.5mm. I can always open 'em up to 3mm later if required but putting material back???
I have to say though that the original rockers
do have a vertical 3mm hole but with no 'O' ring etc