The lifters probably aren't worn so much as they are maybe gunked up. You can try adding a quart of Risoline to the oil and run it for a bit to see if it loosens them up, but when I tried it, it also loosened up the crud around the valve seals and head gaskets and made them leak worse.

I recently made the choice on my '89 3.0L. I pulled the engine and am now putting it back together, but if you only have valve adjuster and seal problems, you can save a lot of money from your quotes (I think) if you can R&R the heads yourself.

I had a good local machine shop go through the parts. Heads were removed and taken to them assembled. They disassembled them, resurfaced the heads, inspected the cams (fine), valves (fine/dressed), valve seats (fine/dressed), valve guides (replaced with updated retainer type), valve springs (fine), rockers (fine), rocker shafts and springs (fine), seals (replaced), cam seals (replaced), valve lash adjusters (replaced), everything cleaned and reassembled - ready to re-install. Total labor was $260 (including guides). I supplied all other OE parts - cost about $150 from the dealer. Grand total (not counting assorted gaskets - about $410. The largest parts expense was the cost of the valve lash adjusters. They can be cleaned and reused in many cases, but I decided to replace them.

My engine only had 131k miles, so I got out for less than an older engine would require. I'd suggest pricing the needed parts and consider doing the tear-down and reassembly yourself if you feel capable and have the down-time.

Good luck,
Frank