You know I never made it through the first post on this thread........ultimate sleeper......that's kind of a misnomer. You want your car to run.......my V8 regal is starting to turn into an ultimate sleeper. I haven't started it in a month!
Unfortunately the intake and headers for a 350 will not bolt on the 7A headed 1986 SBO (small block olds) engine. If you put the earlier 5A heads from 85 and earlier SBO on that engine all the stuff would bolt right up. The 7A Olds engine had hydraulic roller cam and small port heads to improve emissions. The 307 in my Regal Limited started using lots of oil around 92,000 miles so it was yanked in favor of a 79 - 403 with 72 - 350 heads to raise the compression ratio. Had to get earlier exhaust manifolds to bolt on the engine that bolted onto the existing exhaust system since I needed to maintain the catalytic converter. The 4 speed automatic TH 200R4 in your car fortunately is a dual bolt pattern bell housing so will bolt to either a Buick - Olds - Pontiac engine or a Chevy engine. When changing engines a looser stall speed torque converter would add to the fun of driving. That torque converter is a 1700 rpm stall unit and a 2000 stall would make it come out quicker. Just make sure it is for a 200R4 transmission and is a lock up type. Frame pads are a pita to change, but in the scheme of things the least of the engine swap problems. For Buick engine installation just go to a yard and get the engine wiring from a N/A V6 engine for the Buick V8 needs. The accessories brackets and A/C hoses from that V6 car will also bolt right up to the Buick 350 or Buick 455. Things like the starter being on the opposite side of the engine and the distributor in front rather than in back makes getting the harness worthwhile. If you have to maintain the car for emissions you may have to go with an after market intake for the Olds 350 for enough places to mount all the sensors for the computer. At any rate the G-Body is a great car for a number of engine options. Most of us feel a Buick should house a Buick engine . . .
84-85 corvette 700r4 convertor will work is the 2004r (27 spline) the 350 heads are suppose to fit the 307 also 260-307 head intake ports are like 1 inch squareand barely flow enuff for a 260 let alon the 307,thats why the 307 wears out so fast it struggles to get any air in the cylinders thru that tiny intake port
Your using a 86 regal as a sleeper. Everytime any of those a-body cars rev up next to me I look over it very carefully before I race it. half are slow and half are street drag cars it seems. I usually look at he wheels and stance the most. Have fun
If you want to keep it simple and low cost,the Olds 350/403 would be the way to go. It is a direct bolt in.