If the car is as good as you told then go and get it. Finding a date correct 428 CJ can be done - friend of mine at Friendsville TN has a 50 or so FE blocks - no junk - only 428 CJ / 427 : s. I'll let you have his contact information if you want it, he can build you a date correct engine with OEM parts if needed or with some stroke kit to get nice 465 cid for example but have the OEM looks.
If the car has a 351c it is missing its orinal transmission for sure, since sbf and fe has a dirrent bellhousing. How about the rear axle, it's got the N-case intact?
For 35.000 Euros its not the chepest one, but if it's close to concours resto then get it. You can allways sell the 351c 4v, if it is a 4 bolt mains version then there's allways a need for them like the Pantera owners - they want it if its 4-bolt block and with std. or max. 0.030" overbore. A restored true R-code '69-'70 Mustang fetch between to 60.000 - 90.000 Euros here locally. You won't get the VIN to the block but you can a correctly dated parts though - its close as it gets to the orinal.
Good luck for the car hunt!!! Mopar's has a one good thing, they've got the correct bolt pattern 5 x 4 1/2" for the wheels...
I wouldn't say a thing from driveability of a BB car if you haven't ever owned one - HA HAA.
EOM
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corrected typo