True on the O2. Yhe Co Performance cast exhaust comes with 1 x 02 bung in a riser. Optional for 2.

Could make a 02 plate between man and risers for other systems, but would probably ? throw off riser to y pipe connection. Speaking if which, see below

Your risers are going to have to line up perfect with the ypipe. So, will have to get drawings or a big promise. Lol.

Yea im not sure what going to happen with the Y pipe and wont know til I try. If they dont fit but I can make some simple modifications to make it work ill do that. If there is no chance of it working I will go through hull. I could potentially build some custom risers to meet the Y pipe but I think through hull will be less work.

thru hull will decrease you chances of reversion.

Little update on this project, not going to happen as soon as I anticipated with summer quickly approaching here in west michigan. I don't want to get stuck with nice weather and an unfinished boat. I still want to make this happen though so I will slowly be collecting parts and getting everything as complete as I can out of the boat.

Another reason I wont be doing this right away is I would like to do a direct fuel economy comparison between the SBC and LS. Run a couple tanks through early on in the summer, swap the motor and run a couple tanks through with the LS.

I did this with my 1997 Jeep wrangler. In stock form with a 2.5L 4 cylinder and a 5 speed manual on a good day I got 17 mpg. Swapped the 2.5 out for a stock 5.3 and on a good day I could see 20 mpg.