probs after new head gaskets

Hi all,
Newbe here. Backyarder.
'94 es 300, 112k.

Had both knock sensor codes and was overheating every 400 miles or so.
Took off the top, replaced the head gaskets, knock sensors, plugs.
Put it back together, ran rough (4 cylinders maybe?) and died after 1 minute. Now cranks a little but only a few revs.

One prob I had going in was that I failed to put it in top dead center before disconnecting everything, and was unable to do so (couldn't get it out of park) once the intake was off. I decided to paint marks on cams, timing belt, in and ex cam gears, and thought I had it lined up perfectly when I put it back.

So, could be timing/timing belt is off, but not sure how to approach this now. I know I can go back to tdc and then line things up by the book, but I'm concerned the intake cam gear(s) might be off. The cam sits in only one position on the ex side camshaft, and lining that up w/ the marks is do-able, but my prob might be the intake cam being off a tooth, and my markings for it to mesh with the ex cams were done when it was not in tdc.

My ? then, is there someway to assure the intake cam is positioned correctly?

Thanks in advance.
Phil