Exhaust and motor mount questions

Hey, so through my own stupidity, I forgot to crank down/tack in the second o2 sensor plug and it fell off on the highway. Now I have a great sounding exhaust leak. My main issue is where to obtain a plug like that one. I checked the pitch of the smaller plug and its 1.5 on the metric scale, and the opening of the larger o2 sensor hole is ~20.8mm (random). Anyone have any input on what to do?

Also this is the header i bought. http://www.ebay.com/itm/Stainless-Steel-Header-KA24-240SX-91-94-XE-SE-LE-NA-2-4-/230695839756?pt=Motors_Car_Truck_Parts_Accessories&fits=Model%3A240SX&vxp=mtr&hash=item35b68b280c#ht_3400wt_1344

Part two. I picked up motor mounts from sharpe_corners and have yet to put em in. I only have a few hours after work (home at 6:30pm up at 6:35am) and am unsure if I can do the whole swap in one evening by myself. I’d do it on the weekend but I have to go see my girlfriend this weekend as she came down the last few weekends. The point of this ramble is; Is it ok to install the motor mounts and tranny mount seperately?

Thanks a lot guys, appreciate any input.