turbo and frontmount should be OK. Intake I'm not sure - may or may not depending on size, maybe. OEM turbo inlet same I think....
frontmount can prob make work with some custom piping
Cobb AP....I don't see any hard issues moving between 6 and 3 as long as unmarried of course. Soft issues (software lock to 6 or 3) could still be a roadblock - research that with Cobb if it's not in the forum archives, I'd say.
Coilies - I'd be surprised. I know BK to BL three they are transferable with one bolt size difference. Maybe a trivial change needed? Can't say off top of my head. Short answer no, long answer maybe if you.....
Exhaust definately not. Even downpipe is different I think.
I was lucky when my BK3 was up for reconditioning (250,000K, burning oil) I got a very low K BL engine and swapped out. I would consider that kind of minimum $ solution to a bad compression scenario if there's still low K engines around. I'm hoping to see 500000K on BK before I need to seriously think about that again.
I'm going to sticky this thread because I'd like to build a reference area for questions like this at some point.
"Blue Meanie" 2007 Aurora Blue MPS 3 - 18x8.5+44 SSR GTX01 - 235/40R18 Michelin PS5 - 3.5" ETS TMIC - CPE stg 2 mount - HKS/CPE BPV - 2XS inlet - 2XS short shift - Corksport turbo manifold - HT 98 octane tune - Leather/Aluminium handbrake - Momo shifty knob - 7" touchscreen - JDM Mazda Retractable dashtop screen assembly - Bespoke Raspberry Pi Android based GPS/Carplay and instrumentation - 36AH reserve battery and C-TEK isolator - TEIN Street Advanced coilovers 1" drop - Superpro bushings - 220Kw/410Nm.
"Lipstick" 2013 Velocity Red MPS 3 - 18x7.5+48 Enkei RPF1 -225/40R18 Federal RS-RR - CPE TMIC - COBB inlet - CPE stg 2 mount - COBB Stage 1 98 octane tune - COBB shifty knob - 2XS short shift - 2XS turbo manifold.