Evo sporty motor mount dimensions

[Scoobydude]

I'm about to have a motor mount for my sportster machined up for me. I have a Haifley hardtail and the stock rear end to reference and Im not digging the countersunk holes for the lower motor mount because I wanted to use a 3/8 thick cr steel bar stock for mine
Here's Haifley and stock with the long countersunk holes...


Here is what I'm thinking of, although the hole dimensions might change with the furtherment of this question


... On the tc brothers hardtails, there is no countersunk hole and it looks like an idea similar to mine.

I would like some input from y'all as to ...
1.why are these countersunk, and what the reason is(maybe there is an insert for vibration or something..I also see the lower mount on the frame is serrated inside so maybe that holds something)
2. And what size should I make my bolt holes for that mount... Should they be a perfect .50" to .50" match? I'm curious that a perfectly tight fit might not me good for holding two object together that vibrate.

[JBinNC]

On most of the evo XLs, the lower two motor mount nut inserts stand proud of the mount surface and act as dowels, registering in the counterbores in the frame, to locate the motor accurately.

Jim

[Scoobydude]

Thanks for that, I searched around online for a parts manual, since my service manual doesn't show what the parts manual calls "bushings".

Can anybody tell me the I.d. of any Evo sporty frame mount that doesn't use the Countersunk motor mounts on the hardtail. I know that's a longshot question...