The McLaren F1 was originally going to have a Honda V12 but Honda were not keen to develop it, so I get a bit of a kick out of using a Honda powerplant. The J35 engine is 122kg with oil and coolant, vs the LFX 157. Downside of twin engines is the weight penalty, so 75 kg is a big difference. The J35 with a cam grind and head porting has easily made similar power.
My budget is quite low for this project, so as I already have both engines I won't be changing spec at this stage. However the Tbox running twin engines was an idea I was originally going to install in a Mazda 787b replica. I would still like to build a racecar, but a roadcar makes more practical sense and is hopefully less lethal.