I was just looking into porting/polishing my engine, and did a quick rifle through my old RC Car Actions. There is quite an extensive write up in the January '05 issue (you can order back issues from them) on porting/polishing and even retiming an HPI S25. Obviously it isn't likely this is your engine, nor is it mine, but it gives good how-to's and details about why/how. As for tools, they don't have part #'s, but what you want is sharp carbide cutting bits, and stone and rubberized grinding bits.
Looks like they were using this tool a lot.
It is from this page, probably a few of these would do good (the bottom set).

The grinding bits would be from here. I'd probably go for 953.

Well, this is probably being posted long after you've found a solution, but oh well. Later