Hi Cliff, I have experience on T140.
You must have a proper tool like factory one with the 2 pins that fit into tappet block hole. That is a given or you are at risk of breaking block.
Factory didn't seem to worry about tearing o-ring or leaks so they left roughness on most surfaces. We want to do better.
Take a visual look at tappet block where it fits into block & oring groove. Take some fine emery cloth & smooth sides & edge of ring groove. Don't reduce diameter of block or round corners of groove, but smooth them some & they will now feel smooth instead of rough from the tooling.
Do same for bore in cly. Pay very close attention to the small chamfer at top of bore where tappet block enters. This is the prime area that damages oring. Smooth that very well so ring will compress easily as it slides by.
Verify you only use viton orings as they resist leakage much longer.
I personally lubricate the bore, block side & o-ring. I suppose rubber lube is best, but I use wheel bearing grease or even motor oil. Have never had ring tear on install or leak. I don't like dry install. I used to glue top edge but found not needed. Glue top if you want, no harm done, but make sure sealant does not get near tappet oil passages. Late T140 eliminated oiling to tappets so there it doesn't matter.
I set cyl on a redwood rough saw 4x6 board 14" long. I find a place on concrete floor where board sits nice & flat. Set cyl. on this.
Remember tappet blocks don't go straight but slope slightly so keep the angle correct best you can when knocking in. I don't cool or heat anything. Just room temp all parts.
I'm with Hermit 100% about aligning block to cyl best you can. Bolt hole you can be way off & bolt still go in fine. I've seen installed crooked & wear pattern on block ears corresponded unevenly. But is outside of spigots perfect?? I feel better aligning it this way though.
I line up bolt hole by eye & start driving in. I use hammer the size shown in drawing in shop Manual
. I find that works good. Just at least close in size.
When about 3/4 I measure using squareness using straight edge & depth gauge. I put straight edge in tappet block & hold firm to ears. Then use depth gauge to measure to each spigot for cyl bores. Record measurement. I mark block with felt pin so I rotate correct direction.
This sounds crazy but works. Grip the driver tool tightly. Push down hard & turn tool in direction block needs to rotate. Turn hard but only by hand. The continue driving block. It actually will rotate rather nicely as you drive it. Never ever force it to turn. The block will turn only as it is moving! It only turns a tiny bit at each hammer blow.
Go a little deeper & measure again. Check your progress as you go. Sneak up on squareness. When the o-ring gets close, observe it carefully looking for any rubber peeling off. Even a trace of rubber is a failure. Remove block, verify surfaces smooth & get new ring, more lube. Start again.
Often you may miss square when block is seated. You'll hear the block seat as sound of hammer blows will obviously change. There is chamfer on bottom of block so you often can't really see if down home visually. But you can feel & hear it.
So if not square record measurement & for sure use felt pin to mark desired direction both top & bottom of block. Flip cyl over. Again pushing hard down & turning drive block out slightly. Measure again drive a little more if needed but be mindful where o-ring is don't let o-ring rise out of cly. Look at parts before hand so you know where ring is. Memorize that. Now again recording measurement drive block back home. Repeat this zigzag up/down until block is square. 1st one is hard. The next is much easier as you get feel for how much to turn it. Don't give up. With a little practice not difficult. I try for less than .002" difference left to right.
If this is confusing on how to measure PM me your email & I'll send photos of the straight edge & depth gauge. A normal 6" Verner caliper can be used for depth gauge.