Hi mate
The frame number may well be there, mask the surrounding areas and apply some nitromores to remove the power coat in that area, do not use any abrasives.
I should be able to find the chassis number by the reg number but there is a £10 fee so if you can find it yourself that the best way.
And if you do find this it may well be worth the £10 fee to see if it matches whats on record.
To apply for the v5 is easy when you have the numbers, you just send DVLA £25 and it takes a few weeks,
If your bike was registered before 1st August 1999 then you can get away without a visable chassis number for the MOT but you will need to resent the V5 when you get it.
I find DT frame numbers are usualy more visable than the RD numbers for some reason.
Tampered numbers should be reported to VOSA by the MOT inspector so no number is better than a tampered number.
DVLA do not check or use engine numbers for registration but the correct number should be listed on the V5.
Where do you live? if your local and im passing I would take a look or if your passing the MOT staion I work in I could take a look there, im in Hampshire