Rope seal with the engine in the truck is a PITA. It can be done, and there are some tips in search. Just probably not for the 270. GM is a different beast. The trick is to drop the crankshaft while under the truck. So you get to remove the rear main bearing cap. Then loosen all the others until the crankshaft will drop down some. The front cap should not be removed. You want the back end of the crank to move down not drop out. I have also had to remove the bolts that hold the transmission to the Bell Housing and push the transmission back a bit to let the crankshaft drop. Are we having fun yet? There is a tool, called a Sneaky Pete that will screw, into the seal and help remove the 1/2 that is in the block. The same tool is used to tease the seal into the block while you turn the crankshaft to ease it around. I have had limited success with the technique. Sometimes I can get it to work, and other times....well you get the drift. When the seal is in it will need to be trimmed flush at the block. The other half is easy cause you have the bearing cap out and in your hands. Use the manual to help with this part. Again trim flush, put a dab of black sealer on the ends in the cap and re install. Torque all the bearing caps, re install the bolts for the transmission, Replace the oil pan, and dust covers and you are good to go. Best seal is from Best gaskets. Is there a neoprene seal for the 270? I don't know. I have used them in 235's with great success. Much easier to change, and install.
