Your at 9200 feet------------you need a much bigger carb to let in enough of that THIN air without getting into the secondaries, and some very finely tuned jets-The fuel system supply---go back to an engine driven oem type pump----use a genuine Multi sparp MSD---no cutting corners------run more timing advance--with that thin air, there isn't much static compression so spark knock isn't probably happening-----------


At higher altitudes you should of just supercharged a small block---------you will have a hard time getting enough air into that 494------


And also-what are you running for fuel??????????????