Classic & Vintage - Please help with this mystery frame: Centurion suspected but not sure!

Hi,

Picked up this frame from ebay. It is the 1st bike for the year N=N+1 :-)
It has been repainted or powder coated and modernized so the component vintage is not that helpful in determining the frame. There is a serial no under the BB and it fits the Centurion format. Starts with M followed by 5 but it it is very faint it could also be a 3.
Some distinguishing features:

1- The rear dropouts are Suntour GS.
2- Wrap around seat stays
3- Long top tubes lugs
4- Seat post is SR Royal 26.8mm

It looks to be chrome plated underneath the paint but not 100% sure of that either.
I suspect its a Semi Pro but the 5 doesn't match.
Here are the pictures. I reach out to the collective wisdom of this forum for the final determination.
If indeed there is chrome under the lugs what is a good way to expose the chrome again.

Thank you for your help.

Looks like a very respectable piece of mid a 80's Japanes metal. Most of the parts are not original and it is repainted which makes a positive ID hard. Your guess that it a nicer Centution seems about right. It likely has chrome about half way up on the front and rear not the whole frame.

There a section of exposed metal around the bottom bracket. It is shiny. Could that be chrome?
The frame got some love with 8 speed upgraded drive train, rx100 Shimano sti, and is cold set to 130mm.
Between the paint and drive train upgrade a lot of effort was invested. They wouldn't have gone to such effort for a low end frame, would they?

Closest match is this frame:
http://simplicityvintagecycles.com/2012/07/02/1977-centurion-semi-professional-pre-rejuvination/

But could the 5 in the s/n be for 1975?
This would mean the cable guides and dt shifter braze ons were added at the time of the repaint!

I'm inclined to agree that this is probably a 1975 frame that was upgraded with braze-ons during the repaint process. Long point lugs had largely fallen out of popularity by 1985, as had full frame chroming. Dropout eyelets were rare on race frames of this level and most had converted to recessd brake mounts. Certainly, with the exception of the dropouts, the frame is a very good match for a 1975 Centurion Semi-Pro. To confirm, look inside the head tube to see if you can spot where the two, horizontally aligned head badge holes have been filled. If they are not present, it may be a Sekai Competition, which was a virtually clone, made by the same company, but used a head decal/sticker.