uh oh, i see another one of bill's "i am just gonna drive it the way it is" 10 thousand dollar projects brewing. lol
miata's handle nice. get a road dog bar for it to reduce teh cowl shake/flex and it will work a lot better.
before you get too far into pricey jap motor work you shoudl remeber that there are plenty of people who have swapped in 5.0 fords, 350sbc's, and the LS1 fits in there very nicely.
later
tim