Before I grind away..

Hi chaps,
The main things on my recent 90 MOT failure is the rear out riggers on both sides. So, off with the old one and then pause before taking off too much with the grinder. When the new one arrived, helpfully sent by Craddock's, who didn't have it in stock, despite them saying they did, it is stepped. I assume this intended to just slot into the existing hole. However, the diameter of the hole is less than that of the new piece, so it will not just slide in. Do I need to grind back the old so it is completely flush with the chassis, or do I need to knock out the centre somehow? if that makes sense?

the outrigger goes right through, the last ones i did i had to remove the tube through the chassis too

So did you grind away on both sides of the chassis until flush and then does this break the weld with a bit of persuasion?

I had to trim the spigot of the new outrigger slightly to get it to fit. And used a die grinder to clean up the inside of the hole so it would fit in. Took a fair bit of hammering to get in though, but the benefit was that it was pretty solid even before I then welded right around it.

So I am seeing two schools of thought here. One to grind flush and then knock out the centre, or grind down the outrigger and essentially make it fit the existing hole. Hmm, Is the former the better, but more involved method, or is in actual fact trying to ream out the existing hole, more of a hassle?