For 300HP out of a 4.3 V-6. Non-Vortech roller-cam block. One of the early ones. Rebuild with Speed pro pistons Intended for a 350 #PN LW2256-F-060 Hung from The stock rods.(not the same as a V-8), fitted with Milodon small block rod bolts,Wich need to be slightly modified to fit by clearancing the bolt heads. Use the stock crank with sealed tri-metal bearings (unique to the 4.3) fastened with Milodon main studs designed for a V-8. You will need a performance oil pump with a matched performance pickup.
Then either buy some 2.02 heads, or rebuild the old ones to accept 2.02/1.60 valves. Then Comp cams hydrolic roller used with the stock roller lifters. 224/224 duration at 0.050-inch tappet lift and having 0.525 inch lift with 1.6:1 rockers for increased lift. Top it off with a 650-cfm Demon carb and you have 300HP at 5,400RPM and 316 lb-ft of torque. If you want more slap on a blower, or mabe some nitrous, or both what the hey