Front end rubbers....sway bar mounts, tie rod ends, control arms and probably steering rack.  These things are notorious for front end vibrations.  Your strut tops might be stuffed.  Motomobil do nice exchange units, I just sent them some old escort ones and they were happy with that.  You don't need them up front, they give you money back when the exchanges are sent.
 
With rear bearings make sure you get the correct kit, some have wrong thickness retainers.  The bearings are a nightmare to get off since the retaining plate is in the way.
 
For cooling system check that the heater isn't leaking.
 
As for D port heads don't forget you will need a D port manifold as well.  You will probably get a better and cheaper result with a new cam.
 
Rear springs probably need re-setting.
 
Paint is not only about looks.  Chances are its old crazed acrylic which lets moisture through.  A properly done 2 pack paint job is also about rust prevention but for now at least get some polish on it.
 
Check the rear vent drains under the back window, they are usually rusted out and let water into the boot.  You need a mirror to check them, or shove a camera in there and take some pics.  These are pics of mine.

I used the superflex bushes for my sway bar, not as soft as rubber but better than nolathane.  Track control arms are available with rubber.  What is  unclear to me about D ports is whether or not the power increase is across the whole rev range or just at the top.  At least with a cam you can select a profile that gives the boost in the rev range you want.  Yes heater element is a bit of work.  The box has to come out from under the dash and then be pulled apart.

About 10 hp difference - but with Kent fast road cam etc - make the old lump a bit more zappy. The fun with a v6 Capri isn't so much in a power increase for me but the fun of a torquey great looking little rear wheel drive u can throw around and wheel spin for a buzz - a v8 beater they arnt.
I'm waiting for janman (on this forum) to come thru with some juicy aluminium heads

Hope this advice is not too late...................You said in your intro car has lay idle for 15 years (just like mine in pic on your left), but you can't get it to start.
When I found my GTV6 165HP D Port "Wild Plum" sad and alone in its garage for many years in Central Victoria, the first thing I knew to do, as with ANY engine that hasn't "turned over" in 6 months or more, is to remove ALL spark plugs and squirt in a few tablespoons of "LUBE" in each pot (Lube can be 50/50 WD40/10w30 oil, or 100% WD40 if you suspect internal rust/corrosion, even 100% diesel fuel is very good and my personal favourite)........let this soak for  5 mins to 1 hour; pref 1 hr if rust/corrosion is suspected; then add more.  With ring spanner on Crank Front Bolt, try moving crank back and forth 1 degree at a time to free up any chance of rings sticking and then breaking, until you get to a full revolution or 2  of the crank.........if moderate force doesn't budge the crank, STOP! and add 2-3 more tablespoons of "lube" and let sit overnight........then try again next day. 99/100 times you'll be ok and able to incrementally move crank as above.  Once you get 2 or 3 full revolutions and it's feeling free, hit the starter for 5 seconds to expel excess "lube"....Remove rocker covers and squirt new oil all over valves and rockers and push-rods. Don't put covers back yet..... Install Sp/Plugs....... Run engine till you see oil squirting at rockers & valves.... Stop engine and fit Covers.  Run engine till warm and then change oil with a new filter.......time well spent if it avoids a ruined $5,000- $25,000 engine.......Enjoy......NB.........First ensure the subject engine  is safe to turn ACW lest the Timing Chain &/or Tensioner should become dislodged.........if so, only turn CW a degree at a time..........My Capri got this "love" and she re-paid me by starting and running beautifully, and I then drove it hundreds of kilometres back home, purring like a kitten, if I ignore the slightly "burnt" valve in one pot and the noisy water-pump that stopped leaking as soon as it hit the highway!...........I also topped up the stale old fuel with 10 litres of "Shell" 98 VeePower which worked wonders !

spud15

I'm waiting for janman (on this forum) to come thru with some juicy aluminium heads

Jamman, not Janman
 
The heads will happen spud, Not sure I will be posting photos on here though.
 

Capri home:

wow - how many are still out there? they just keep popping up -

Certainly looks like a very good base to start from. Could be a good rolling resto, rather than doing a complete makeover.