hey hellman, thanks for the remark on my camaro
Glad I could help you out, adding ignition cables will make a huge difference in the end.
Well the engine is the same, the chevy big block 454, but the intake, injection system and the valvecovers are custom, "tuning" parts.
I think you should go with the custom version aswell
As for giving the engine a realistic touch there are many quick and easy things you could do to make it stand out, adding ignition cables is one thing.
Kit engines are usually badly engineered IMO, the fitment is many times horrible but many modelers don´t seem to care.
Sand down and dry-fit all the parts to make sure it all fits together and final assembly will be a lot easier.
Btw DONT USE TOO GLOSSY PAINTS!!! I hate when a engine looks like a big lump of dried paint, the engine may have a certain gloss in 1:1 scale but on a model it will just look cheap IMO. Use some good metalizers/metallic or gray paints to give the engine a realistic touch, you could also add a "wash" to highlight the details.