there are sites that have the diminsions of engines and drawings--cut out a templet and see if it will fit between the suspension towers and another front/rear to see if it ll fit between the firewall and radiator----

Once you have determined that it won't fit----put the hood back on----

Probably the most compact v/8 is ford 302 ---do the same template manuvers--if it'll fit then you can look at some in between choices and I'd recommend the alum LS gm engines--for performance, economy and emissions

If a V8 doesn't look promising. how about a V6? or some of the new 4 cyl super/turboed engines??