Thanks @Phak 1
Was it drilled round 7/16 or 1/2" - and did you use carriage bolts?
I can only imagine the 1/2" is to clear the square on the 7/16" carriage bolt shoulder
If indeed it was 1/2" round (and it had to be if the holes were round and used a 7/16" carriage bolt) can you recall further, does a 7/16" carriage bolt fit through that 1/2" hole with the timing cover in place?
I'm wondering if that 1/2" hole allows for better angle of entry to get it through with the cover in place ....
edit - clearance for a 7/16" bolt is 29/64"
For others searching I found this excellent thread - https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/908168/1.html
- with extremely good info referenced to Lonniec (it's an inserted quote in a DADS50 post) and some terrific pictures by Denny Graham
Lonniec reported (and there's an image) that showed his installer ground the head of the bolt for the passenger side to get it in under the timing cover on that side.
Also in an unrelated post on Alternator Mount I happened across this image from @Poncho52 which is an interesting idea of using the nuts on the top side for the centre bolts
Image only shows the drivers side though - there may still be an issue with the passenger side, at least with a view to using a nylok nut.
WIld idea - I'm toying with the idea of making a rectangular slot on the timing plate on the passenger side which would allow the carriage bolt to slide in under the timing cover; the drivers side would be regular square.
To make, drill 7/16" holes, square off both holes, then file futher on the passenger side to create a slot, just wide enough (TBD) to get the bolt in place.
The side to side and final position of the passenger side bolt would be constrained by the driver's side bolt and once torqued, even the passenger side would likely be a non-issue in that plane.
And the vertical integrity for me would be better than grinding the head of the bolt.