I am wondering if the following is possible/safe to do:

I was thinking of getting this 2" dual receiver adapter to put on my 1
1/4" hitch (on a 99 grandprix gt)...

This is the 2" dual adapter:
http://www.cabelas.com/cabelas/en/templates/links/link.jsp;jsessionid=WHECS01NKE
0YACWQNWQSCNIK0BW0EIWE?id=0038402521997a&type=product&cmCat=froogle&cm_ven=data_
feed&cm_cat=froogle&cm_pla=0530110&cm_ite=0038402521997a&_requestid=14726

Obviously to make this work I need the 1 1/4" to 2" adapter as well:
http://www.cargogear.com/oneiteminfo.aspx?partnum=SW64003

I would use that combo with these two:

Bike rack:  Allen Deluxe 4 bike
http://www.amazon.com/gp/product/customer-reviews/B000LHP1VA/sr=8-1/qid=11852891
75/ref=cm_cr_dp_all_helpful/104-2740971-4919918?ie=UTF8&n=3375251&qid=1185289175
&sr=8-1#customerReviews

and this cargo carrier:

http://www.cabelas.com/cabelas/en/templates/links/link.jsp;jsessionid=KKSVMIES3T
PACCWQNWSCCNQK0BW0KIWE?id=0006492510253a&type=product&cmCat=froogle&cm_ven=data_
feed&cm_cat=froogle&cm_pla=0530111&cm_ite=0006492510253a&_requestid=31580

Any thoughts on the ability of the hitch itself to handle this load,
with 4 bikes and some luggage on the luggage rack, obviously my car
would need to be able to handle the load, I'm guessing it may kill a
bit of gas mileage too.. perhaps not the best combo, at least for this
vehicle..

(the hitch on my car is rated at 350 lbs of downward force, 3500 class
II loads overall).