And as was mentioned they were available in multiple mounts. You can find one for your Rollei 6008 here.
Wish they had one for the hasselblad!
When I bought the Bronica, there was no Google or E-Bay. My last purchases were the 500 mm lens and 2x telextender.
I've gotten some beautiful shots at 1000 mmm, and a lot of questions because the total lens set reaches nearly to my toes.
I want to see a pic of that setup. Haha
6x7 negs/trannies are 400% bigger than 35mm; in the 645 format, a little smaller, but still a whopping improvement. At printing, there will be no discernible difference, save only for any faults introduced by you e.g. exposure errors, focusing off, etc.
There is an endemic quality of imaging at for either of the MF sizes (including 6x6 and slight variations) and print quality will be uniformly excellent, in terms of viewing to whatever size you desire (currently I'm printing at 81x61cm).
I personally don't have much use for 645. It's not different enough from 35mm. My 16MP digital can already print a 20x24" just as well as my 6x7; but I can hold my 6x7 transparencies up to the light and people go "oooh", whereas the 645 and 35mm transparencies just make them squint. :)
If you are interested in very smooth tonal gradations of grayscale, and if you are interested in as little grain as possible, you should carry the largest format camera around that you are able to carry, and you are able to use with as few limitations as possible to what you wish to achieve.
If you are interested in only getting a good picture, you carry around the camera that you are intimately familiar with, and don't give a dime whether there is grain in the picture or not, because you know that for most purposes, even 35mm will be more than good enough with super careful processing and printing.
Likely you're somewhere in between, or maybe even do both side by side. Then you have to compromise.
There IS a difference between 645 and 67. No question about it. You will get 'better' print quality from a 67 negative. The real question is how much that really matters to you, and whether you're prepared to only get half the photographs in the same amount of film, and if the extra bulk doesn't bother you.
You COULD purchase something like a Fuji or Mamiya rangefinder and shoot 6x7 with a camera that is very light, portable, and extremely capable.
Good luck with your choice. Whatever you pick, make sure it meets your demands for portability, picture quality, shooting speed, etc.