Over the last two decades or so when we have been too busy to restore our 105 cars, we (most of us) have opted to enter concourse and show and shines events (to win trophies or for what ever reason), using more modern cars (not 105s) And we wonder why in general it takes decades to even know what the correct interior and exterior looks like on a 105 car.
To remove the BAT car from it's current hybrid state there are a few things you can do.
If the factory lists the interior of the BAT car as coming with a Bertone DeLuxe, leather interior then this is the path I think you should take (Red or dark brown), see the numerous posts here on AlfaBB, there is even a company that will do the perforations for you in the US. Otherwise if the car came in vinyl, but you want leather see my previous statement. You will need one stainless trim per door for leather door cards. If you don't mind vinyl the car can still be redone in reproduction vinyl for the seats and door cards select one of the 2 colours you can get here is just one company's offerings. Not sure if the reproduction door cards use stainless trims, if they don't have to find two more stainless trims and have them made up. Vinyl colours are light brown, black or grey.
the door cards come in black or brown, for grey you have to make them up.
You definitely need a set of rear seats for the frames and foam
The B.A.T car shows us in 2019 a 1600 engine will only last if you build it to last, regardless of who could have carried this out in it's life. There are some engines that have serious issues while others that don't. It's not as if members on Alfabb will not assist with advice and recommendations, but you have to start from scratch with a 1600 engine. Now with the 1600 BAT engine partly disassembled it needs a cylinder/ valve train and probably best to review/reuse the block if possible as 1967 blocks are hard to come by.
Check the crank, if it's going to end up at 10, 20, 30, 40 thou find another one (race ones are around for $$, get some performance pistons and liners and conrods etc while you are at it. By the time you go through this car with the needed repairs and some optional performance upgrades as per factory parts manuals and FIA homologation for 1967 GTV /race rules, for diff and gearbox I think it will get close to a valuation of ~$80k by the time you finish in 18 months time.
Good luck to the seller/buyer