I believe the slide is drilled and tapped and the rib secured with hex bolts. I would further imagine the original front sight has been ground or chopped off. I think colt_saa would know better as he's got one.
If it is altered and an I cannot imagine it is not, I couldn't see MOST people spending more than $800 on a 52-1 that has been altered, but I've been surprised enough times to know that there is a buyer for most any and at prices that would astound me.
Other items in the conversation. Across the market, the 52-1 trades slightly under in price to the 52-2, almost surely because some are leery of the old style extractor which they deem to be fragile. The extractor is a whole other conversation, let me just say that I'm personally not scared of it and my 52-1 is an amazing and fully functioning pistol.
The weight, again -IF- marked Smith & Wesson could probably sell very quickly at $100, and these days perhaps higher.
Two mags is solid, the magazine market for 52's is absurd and royally out of control, so they are extremely expensive.
For my first ever 52, I would pass on this if you cannot get out the door for a grand or under. However, if it runs right AND you can source or make HBWC ammo for it, you may shoot it and not care whatsoever you paid, as 52's are phenomenal!