If bayonet-equip-your-shotgun-you-must, be attentive to the subtle details provided by the photos up post... Namely, the old-skool AR/M16A1 M7 bayonet is a
real bayonet 
While the current M9 bayonet is an excellent
field knife.
Also, you should know that most bayonet-equipped shotguns were intended to also have a heat shield on the barrel, with the idea that you would have been shooting the shotgun furiously before coming to grips
mano a mano at extreme-close-"give-no-quarter" bayonet distances. Usually these heat shields are of the perforated sheet metal variety. The old WWI-era Remington Model 10 had an elegant and practical
wooden upper hand-guard, that, sadly

is not made by any aftermarket stock designer for more modern shotgun designs.
Also, in researching the Model 10 from Remington, I made the interesting discovery

that Remington had on hand a variety of bayonets already from past contracts. So... Remington took all the rolling block 7x57mm rifle bayonets that it had once sold in Mexico and other Latin American nations--a handy knife bayonet with a hooked quillion-- and developed a mount for the Remington Model 10 to accept the bayonet--otherwise useless after the mass adoption of 7.65mm and 7mm Mauser rifles throughout the Américas. And... wait for it .... All the old Russian Czar-contract M91 lock-ring socket bayonets from the Bolsheviks-in-power-stop-sending-Mosin-rifles laying about the Ilion, NY factory.

Now, the spike bayonet on a shotgun has salient drawbacks, namely, that it can be grasped by a zombie, erm, uh, I mean assailant

and wrested from the intended user's grasp, which a blade bayonet typically precludes...Ouch!... But I have to say that installing a Russian Mosin-Bayonet, a pointy 17-inch steel spike--would be a heck of an accessory, even if of limited utility and a liability in defensive or tactical terms. As you might expect, I have contacted aftermarket parts folks and asked that they develop, or redevelop, just such an accessory for the modern Rem. 870... They have been polite, although once I'm off the phone, they probably think I'm a bit deranged or mad....
Anyhow, a drill will remove the dimples, and some dribble-on blue will prevent the holes from rusting constantly... In my case, a 4+1 guy, I don't worry about the dimples. Older shotguns, fortunately, don't have 'em.