360 to a 408 how much quicker

Well, I actually had to ADD weight to get it to the class minimum weight in IHRA J/Crate Motor which is 3,530 lbs with driver. I usually race at between 3,540 and 3,580 lbs. I did remove some stuff allowed under the rules, like wiper motor, radio, heater core, blower motor, etc. which allowed me to put more weight in the trunk, like the battery & weight boxes, where it will do the most good, as well as frame connectors and 8 pt. roll bar.

Carb tuning with jets, pump cams & squirters is important. Jet for MPH and change squirters and pump cams for 60' & 330'.

Shop around for a good engine machine shop. They deserve a lot of credit. But the more attention to detail, the more expensive it is. Also, remember that some stuff is not "street friendly" for dual purpose cars, like low gears, loose converters, lots of cam duration, low tension rings, very lightweight wheels, etc. Needless to say, you have to consider the attention/rebuilds required with more radical combos. I try to swap out/freshen engines after a season or two. Some hardcore class racers do it much more often.