I have used as in Post #2. Also an aerosol - can says "MG Chemicals 8329 Epoxy Mold Release". For most release that I have used - waxes or spray on - I started to always do twice - in case I missed areas. Most recently had to set a bedded rifle outside in minus 30 for about 45 minutes - that allowed it to be separated - but was all on me, as I had inadvertently created a mechanical lock - was not "stuck" as it looks like in your picture.
I have epoxy bedded several Rem 788 like yours - several Mausers, etc. I do not recall leaving the scope on to do that - that should not affect the epoxy, but might be in the way about getting release agent on - I found that epoxy gets "everywhere" - even where I do not expect it to go - so I apply release to most all the metal - even where I am not really certain that it will be needed. I also put masking tape on the stock where I do not want the epoxy to stick - outer surface, inside magazine well, etc. Perhaps was "old school", but I was shown to have epoxy quite thick - so gouge out lots of wood behind recoil lug - around action screw bearing surfaces - maybe waste of time, I do not know.
Older stuff was PITA - very runny - occasionally had to make dams to hold it where I wanted it - like modern liquid Devcon - runs everywhere - more modern Gel stuff tends to stay put, better.