Hi Lon,
For reflex sights, you could try the below which was my solution when I wanted to put an optic on a mauser action which was not drilled and tapped and my eyesight sucks too badly for irons.
I ended up using a mounting block from JP Enterprizes (fits the Leupold Delta Point, Delta Point Pro, Shield RMS, Shield SMS, and Redfield Accelerator maybe others) and can be machined to fit in a dovetail (Perhaps if you remove your irons you will have a handy dovetail, often can be drifted out)
Block where the base is machined to fit your dovetail (
https://jprifles.com/buy.php?item=JPA-GS)
Then with the adapter plate, sits on top of the block (
https://jprifles.com/buy.php?item=ARR-JP/DR)
It will accomodate sights with the Docter pattern footplate (Docter / Noblex, Leica, Kahles, Burris Fastfire and possibly some others I'm missing)
I swapped out my express V at the back of my 9.3x62 for a reflex red dot sight, started with a Burris Fastfire but swapped to a Leica Tempus for the smaller dot.
Original folding rear express sight in dovetail
Block milled to fit dovetail with adapter plate for Docter footprint optics:
(Sorry is rather grainy image - make sure smith fits facing forward, adapter plate seen extending rearward)
Image of block with a grub Allen head grub screw drilled and tapped through it. On a high recoiling rifle I was advised this might be a good idea to stop the block and sight walking / drifting sideways under recoil. (Should think this would apply to a slug gun too)
Burris Fastfire mounted to block
Overall view of rifle – put a leather cheek riser on the stock just to lift sight like a little agter some shooting.
Really bad attempt at photo of sight picture (Actually looks much better!)
Any questions please don't hesitate to get in touch and will help in any way I can.
Not tried on a hunt yet. Survived a couple of big boar comps and a ~40rd range session at the H&H shooting cinema. Hopefully will us on driven boar in Croatia this weekend.
Scrummy