The only difference in the hyd roller blocks in the LA versions are teh bosses on the cam bearing bore tops for the factory spider setup. I tried in 1990 to use a 340 block and a hydralic roller setup in it. It failed is the best way to put it..lol. Gooddy, if your block has a fuel pump boss, and the threaded bosses on top of the cam bearing bores, you have a regular LA hydraulic roller block. Far from rare, but very desirable. Hydraulic roller cams are a nice compromise, but they have limits. Lift must remain semi conservative, or the lifter will block off it's own oil supply at full lift, and it will collapse. It's also rather heavy, as opposed to any other lifter available. So it needs good springs, and the springs cant be too heavy, or the lifters collapse...lol. That is why you find most performance hydraulic rollers are within a certain window of lift and duration. They cant go bigger and stay functioning. They are less money to start with, because you dont bush the lifter bores, but you do ned the spider setup. I got mine at a dealer "back in the day". A JY or jobber parts store can get them now. The cams are still made from a steel billet so they wont wear off from the roller, so they cost about the same as a solid roller. Pushrods are shorter, so you need those for the setup too, and if you have head work done, you may need custom length ones made. Goody, you already know about teh performance. From "softest" to "hardest" hydraulic, hydraulic roller, solid flat tappet, mushroom flat tappet, solid roller. Each one will make more power than the previous, the last 3 can sacrifice low end for peak power, and cost more. The rest is up to you. How much can you spend? What do you need to have for performance? How much maintenance do you mind doing? What kind of fuel are you running? What about head choice?