kemo,
It's hard to know where to begin. There are SO many opportunities to do something wrong when machining, selecting parts, and reassembling a T Series engine which would result in this kind of seizing. Your best bet is to start pulling off pieces one at a time until itr frees up, at which point you'll have found the culprit. Start by removing the sump (oil pan) so that you can remove the flywheel. If that doesn't free it up, remove or loosen the connecting rod bearings one at a time. If that doesn't do it, loosen up the main bearing caps. It may help to remove the timing cover, remove the chain, and see if the camshaft is frozen in place. Installing the cam and it's split bearings is very tricky, and I have seen otherwise very skilled mechanics mess this up. Somewhere along the line you will loosen or remove something which will cause the engine to be able to turn. When you get to that point, DON'T TURN IT! That's because you don't want to loose the relationship between the crank and cam, cam and distributor, etc. If you understand all these things, and have a manual, then go ahead and tear into it. Otherwise, let me know what you find.
The fact is, I've done a LOT of these engines, and believe me, you gotta stay in practice to get them right. There have also been wrong machining specs published for the crankshaft for many years, which would make for the connecting rod bearings fitting way too tight and locking up. Let me know, and good luck. If you'd like to contact me through the private or email options, that might provre useful.
Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon