help in my hp

i got and 1981 f-100 inline 300 six alll stock with a 4 speed and i need sum more hp out of her but i dont want to do ne cam work................ bout how much hp gaine will i get if i take my cadilac converter off? and if open my exhaust up? will i be able to notice any differnce in the take off.. the endine has just been rebuilt from ford so the engine is like new runs smooth. i have no problem runnin 90 thats as far as my speedo goes i might be goin faster so i dont no ................. NE MORE HP GAINE YALL CAN THANK OFF? .......thanx for the help

GET WITH CLIFFORD PERFORMANCE CALL AT 909.303.2333. THEY'RE IN CA. GET SOME HEADERS, NEW INTAKE AND CARB(S) THEY HAVE 'EM