New guy, advice would be hot...

Hi all, I just "bought" a 90 civic si with some mods and was looking for some advice on the mods. as i said the body is a 90, however the block is from a 95 1.5l (8 valve) and the head is from a 96 1.6l (16 valve). I don't know if this is a common thing to do. but I was wondering what i would need to know about it to have my car run well. I do have the original 8 valve head to the block. the main problem is that right now the car sounds like it is out of time and after a few moments, the engine light comes on and retards the timing. any advice you all have would be greatly apreciated. Oh, also, I am something of a mechanic so don't worry about being technical, I just have experience with 4x4's. this is my first honda and I wasn't sure if i needed to know anything specific. thanx.