In my mind, the trouble (and risk) is all crossflows are likely worn out these days. They're 20yrs older, with 250-300,000km +.   IMO, any replacement sec/hand engine, could have a worn cam also? Use of modern Synthetic/Non-Zinc engine oils in flat-tappet engines (aka crossflows) are probably not helping.   Yes, could definitely use a Micrometer to measure cam lift, and compare with the factory specs. Moot point though, as if the pushrods are straight, then either cam and/or lifters are toast.   Crossflow 6cyl's (and flat-tappet Clevo's/Windsor's too), need 15w/40 or 20w/50 mineral oil IMO. Easiest way I found, is to use diesel grade mineral oils, and double check the zinc content from manufacturer specs.

I used a T-handle lifter removal tool for my lifters.   Initially to get them out, I applied a hammer type force downwards using my palm on the tool handle, whilst at the same time, applying upwards tension on the handle with my other hand.   I later learned that the trick is to rotate the lifters, as you try to lift them in or out. (they're an incredibly precise fit)

most come straight up, some need poking along a bit to the bigger opening.
you are only going to need to check a couple, if one's stuffed, its' game over for that cam, then in my opinion i'd fit another engine (crossflow) to just be done with it sooner.    doing an engine conversion i like to have everything  ready to go, i don't like pulling a running car apart for long, otherwise it snowballs into an unfinished project easy.    fitting a cam with the engine in the car sounds like a nightmare to me, but it can be done.    i'd sooner pull the engine out. (engine out in an XF with the trans still on it is easy, can be done in a few hours if you are set up for it. i used to start undoing stuff friday night, wake up pull the engine out before lunch, and bolt the replacement engine up to the gearbox etc and complete it as much as possible *changing welsh plug behind flywheel and having new hoses, belts, oils etc ready to go. then after lunch drop the engine in the bay and do up all the under side of the car first .. exhaust, tailshaft, gearbox, engine mounts etc.. then sunday i'd just do all the easy stuff and test drive it before it went back to work on Monday good for another 50,000km of zero maintenance other than oil changes.      basically a piece of coathanger would be good enough. sit a pushrod in and get a measurement of how high it comes up and down..  do it same for others, if a cam or lifter is wiped it's going to be 1mm difference pretty confidently. could likely hold a ruler up to the side and see how much the pushrod travels even for 1mm ish  change

If I got a micrometer how would I check the lift on the cam? 

Ok I'll give it a go. Also how do you get it out past the head

they won't be mushroomed, it will be carbon build up on them. 
just work them up and down as much force upwards as you can each time, they'll come out.  if you can rotate the engine a little to put that lifter at the lowest position first, it will get sort of a run up in a yank to pull it out, i don't think you'll get much spray down the side of it, it will just need working up and down.     

Well I went at it some more today and checked the valves. I hit it with a dead blow and it was perfectly free, however the lifters are a different story. I worked them up and down but couldn't get them out my guess is mushroomed faces on them. After throwing the valvetrain back together it ran the same and the vac gauge still showed a missing cylinder. I noticed some glitter in the oil sitting in the rockers while it was running so that doesn't seem good. I reved it and managed to get the cylinder to even out at about 3000 (you can see it in the vac gauge) but it was hit and miss. I noticed that it was easier to hook into the lifter on the intake valve with there seeming to be more space for the tool I made to go in so it might just be a sticky lifter. Any advice on how to get the lifters out?

I can imagine... When my XF was running poorly, I drove it up the street to test, and it barely got out of it's own way.   I'd suggest to get it running nicely first, then decide. It's a big expensive undertaking to swap in other drivelines and have it daily-driver reliable. (especially these days, with rising costs, etc)   It should be brisk and torquey, but not certainly 'fast' like a modern vehicle. World's cheaper/easier to diagnose/maintain and repair though, and I'd choose that any day.  

From ur video angle, it looks like no.1, no.4 and no.5 intake valves aren't opening correctly. Either partly bent pushrod/s (remove to check) collapsed/stuck lifter, or worn camshaft.   I'd also see what the vacuum gauge reads, now that loose pushrod is fixed.   If u have a lifter removal tool, with some maneuvering, u can remove the lifters without undoing the cylinder head. Same for the camshaft. The radiator/AC condenser needs removing to get the camshaft out though.   With my XF wagon, I removed each lifter and disassembled/cleaned/refitted them. I had x3 bent pushrods, all on the intake side.          

Around 20-25nm I believe