I am replacing the head-gasket in the wife's 98 Altima. I have the Haynes guide and everything has been going well.

However I did notice that the heads and timing chain seem to be slightly different, all the guides are gone, marks on the gears and it is a single chain, not the double chain that I have been seeing in the guide. I am curious what head I have in this car now.

Also... this may be a little oops but any tips might help. I removed the head and kept my own timing marks (still set to TDC) however the lower tensioner has made it impossible to get the upper timing gear back onto the head. Any tips to getting this back on? (I don't know how I can get the crank pulley off with this upper gear off to get to the tensioner.

A quick google search showed up that the single upper chain is from a 2nd gen ke24de. 2001-???? So it seems that our assumptions are correct that this was not the original engine for the 1998 Altima. We found marks on the timing gears and all the guides gone. So this was not just a replacement head or timing/head-gasket done in the past but most likely a junk-yard engine dropped in some time in the past.