300 6cyl in 1980 was smogged horribly and came with a 1barrel carb , and intake/exhaust manifolds made for a tractor not a road vehicle. 120net HP comes to mind! scary low power and scary poor fuel economy.
that said, I too think you should stick with the 300 6cyl, but change the air/fuel in, and exhaust out.
Offenhauser 4barrel intake, w/OEM EFI 4.9 exhaust manifolds. they look like 3into 1 headers and make dual exhaust with an equalizer pipe a breeze. 500cfm 4barrel carb.
efi 300six came in E150s 1987-1991 so some of the parts needed would be OEM and reproduction.
the 300 6cyl is an underated engine with huge untapped capabilities.
you are paying Euros for your fuel, mods to the 6cyl may just double your fuel economy ! especially if you can find a 5spd manual for it.
if you are stuck on the V8 swap, 302 and 351 W were both used in that vintage, 351C has the same small block bolt pattern as the 300 6cyl, but motormounts would be custom, 351 M was offered in the Eseries, but not common. 1981-1984 if my memory is working> they share the same bellhousing pattern as the 460, and will be a hard bell housing for you to find in Europe !
stick with your 6cyl untapped tower of power
good luck on your project, I have an 86 E150 shorty and am planning a 460 conversion, but mine has a burnt engine and firewall.
