its not as bad as you may think, but you do need a plate to lock the cams into place . you could have th head checked , but if it aint broke then dont fix it. my car had done 194000 miles on the orig engine when i sold it.. it also had 389 bhp . i carried out the conversion circa 170 ish . i had no problems. my point is , its more about the life it has had and if its been looked after. a stamped book is great , but you need reciepts to go with it .