If you guys are looking for Alloy CR tanks you need to check out Greg's work at Ohio Cafe Racers. This is from his website:
OCR CB350 Alloy GP Gas Tanks
For all 1969-1972 Honda CB/CL/SL 350 twin cyclinder bikes. Also can order tanks to fit the CB350F and CB400F bikes.....and can special fit our tanks to the CB/CL 450's.
* All alloy 4043 aluminum construction
* Hand hammered to replicate the alloy race tanks used by the Honda factory race teams of the 1960s
* Polished alloy Monza caps
* Fits to factory frame mounts
* Ultra lightweight, for racing or cafe racers
* OCR Alloy Tank Capacity: 3.7 US Gallons(Stock Steel tank capacity is 3.2 US gal)
He is going to start offering CR 750 tanks as well as the CB 360 tanks. Shoot him an e-mail, the tanks are awesome, super light and cheap by alloy tanks standards. Plus Greg is a stand up guy! While I am his friend I do not get a cut of anything, just dig his work (wish I had that talent, he is teaching me how to weld, Aluminum Sucks to weld!). If he would have been making the CR 750 tanks a year ago, I would have got it instead of the BCR Kit (don't get me wrong I love Benji's work too, top shelf also). Greg's tanks are far more superior to the one offered on e-bay earlier in this thread. Just my 2 cents....