you can use a PZ22 carb from your briggs dealer, its what is being used on the animal right now, jet kits parts etc all from dlr. EC birt has manifolds to match to the newer wide bolt (or three hole) flange.
If this is the I/c block im thinkiing of the exhaust seat is stellite, very hard, a neway cutter will have trouble making the seat round if its warped. you may have to have a auto machine shop grind on it. looks nice there.........guys these things run good with the internal your discussing
get a new set of valves and billet lifters, mock then up youl need to grind to set clearance.
raptor parts interchange, I used a 03sscam, 3hp flywheel, and a arc head, copper gasket, the compression is very high and its hard to pull over, gotta get it right or it yanks back....mill the deck after you shave (Trenching) the eyebrows. if you dont get a good head, a thinner gasket and the milling will help. I dont believe lifter bore welding is neccessary if you use the "ss" cams i think they are the limit. thats my .02, have fun guys
i forgot to add...i used the h-d springs minus the inner spring too,
I have a spring pocket counterbore, maybe I can send it to you guys. just a small cut, with a hand drill really helps keep the springs centered up. pm me if intereseted.