the cost is leaning more towards an R5P7 as that would be very close by the time all is added up and they MPH of the records isn't cost effective most likely. Great to have the info though!
R5P7 would make the most sense, sbm or bbm your choice is pretty much 340/360 or 361 or a destroke bigger block. If going production engine I'd probably go 361 bored to 371.