your exhaust diameter won't make a difference.

the engine mount insert kit is well worth it in my book. they are polyurethane pieces that fill in the gaps of three of your engine mounts. there's one for the rear mount, lower tranny mount, and a/c bracket mount. this will stiffen up the mounts to prevent them from ripping and make your engine for sturdy.

on my first swap, i didn't buy them, and two of my mounts started to rip.