....regarding German TUV from what I hear it is around 300eu? Maybe I have wrong information. Also I heard that there it is not that difficult to pass and it takes one day to do it?
If the bike/frame was street legal once, it is not more then 100€ and 2 hours or so. If you built the frame yourself (they take it as that even if you only changed something on the original frame between head and swingarm), it's almost impossible. They want a couple of similar made frames to crash them to find out if your creation is safe. But even if you built them their 5 frames only to get 4 of them crashed, it would still be a new vehicle, so the engine you're using would have to pass newest norms etc.
Impossible
Are you sure in that. Because like Yoss wrote there is a lot of people reexporting bikes to Germany just to pass TUV because it is easier... bikes with have modifications. I see also there is a lot of customizers in Germany(probably the most in EU), not just for bikes but also for cars, and they are doing some pretty heavy modifications to frames. Also I know a guy who has custom shop for Harleys in Germany and he is doing some crazy modifications including frames. He said to me it cost him around 300eu to pass all the things... And he is doing customization beyond recognizing original bike.
Can I have the contact to that Harley guy?
Yes, you can modify almost everything on your bike and get TÜV - but it still has to be the original main/front frame with it's frame number, which was once registered before or has an EU-certificate. You can change the rear part under the seat quite freely, if it's done correctly. A typical example is the hardtail mod on Harleys. I know bikes where there were small modifications done to fit another engine which means modifying the front part of the frame. Those welds on the main frame have to be done by a certified welder with certain papers. Trickier is the change from twin-shocks to cantilever. I doubt I would find an engineer nowadays who legalizes such a change. Maybe there is a TÜV-engineer who "has a blind eye" for certain mods on the main frame, I wouldn't deny that. If you reeeaaally know him well....
But if I come to visit them with my own recreation of an egli-type frame and my genuine ELI-001 framenumber
, I have to pass all those tests on strength, welding and so on (maybe a proper computer analysis of the frame strength done by some certified engineer will do)the costs will rise to thousands, maybe ten-thousands...and the bike will be a new bike with all the safety and ecological requirements of today. There is no way to get a CB750SOHC engine in a newly built frame as far as I know. But I would love to get in contact with someone with the right connections