Whoa whoa...
I'm making probably 220ish at the crank with a stock 3.5, stock, cam, 8.5:1 compression, basic port matching and a damn good exhaust on my race car.
350-400 hp is very easily achievable on a Rover V8. It can be punched out to 5.0 and with Wildcat heads and a good injection system (I'd not mess with carbs) you'll see 400 hp and probably do it for $5k.
I woulnd't give up on the Rover V8 yet. I can pick up a Rover V8 block bare and carry it easily - all together it weights around 300 lbs. TOugh to be beat power to weight wise.
You can get a Rover 5Ltr from a TVR and have a lot of change out of 5k.
Have a peek at some rover blurb
3.5
The initial Rover version of the engine had a displacement of 3,528 cc (215.3 cu in). The bore was 88.9 mm (3.50 in) and the stroke was 71.0 mm (2.80 in). It used a sand-cast block with pressed-in iron cylinder liners, and a new intake manifold with two SU carburetors. The Rover engine was heavier but stronger than the Buick engine, with a dry weight of about 170 kg (375 lb). It was first offered in the 1965 Rover P5B saloon, initially making 160 PS (118 kW; 158 hp) at 5200 rpm and 210 lb·ft (280 N·m) of torque at 2600 rpm on 10.5:1 compression.
3.9/4.0
The 3.9 L Rover V8, a bored-out version of the original 3.5 L engine, was used in several Land Rover vehicles, TVRs, and the MG RV8.
Land Rover used a 3,946 cc (3.946 L; 240.8 cu in) version of the Rover V8 through the 1990s. Bore was increased to 94.0 mm (3.70 in) and stroke remained the same at 71.0 mm (2.80 in). Revised in 1995 (and thereafter referred to as a 4.0 to differentiate it from the earlier version, although displacement remained the same at 3946 cc) with a new intake and exhaust system, extra block ribbing, revised pistons, and larger cross-bolted main-bearings. The 1995 4.0 produced 190 hp (142 kW) and 236 lb·ft (320 N·m) .
Production of the 4.0 ended in 2001. The final version of the engine, used in the Land Rover Discovery, produced 188 hp (140 kW) at 4750 rpm and 250 lb·ft (340 N·m) at 2600 rpm.
4.2
Land Rover extended the 3946 cc engine for the top LSE specification of the Classic Range Rover. The 4.2 L engine had a displacement of 4,275 cc (260.9 cu in), and used the crankshaft castings from the failed "Iceberg" diesel engine project. Bore remained the same at 94.0 mm (3.70 in), while stroke increased to 77.0 mm (3.03 in).
4.6
In 1996, Land Rover enlarged the Rover V8 to 4,552 cc (4.552 L; 277.8 cu in). The bore remained the same size as the previous 4.0 at 94.0 mm (3.70 in), but the engine was stroked by 10.9 mm (0.43 in) giving 82 mm (3.2 in) in total. Output was 225 hp (168 kW) and 280 ft·lbf (380 N·m).
Production of the 4.6 ended at Solihull, UK, in 2002. The final version, used in the Range Rover, produced 222 hp (166 kW) at 4750 rpm and 300 ft·lbf (407 N·m) at 2600 rpm.
The last mass-produced application of the Rover V8 was the Land Rover Discovery, up until the vehicle was redesigned in 2005. It is still used by some hand-built sports cars built by some independent manufacturers.
5.0
A 5 litre 4,997 cc (4.997 L; 304.9 cu in) variant of the Rover V8 was used in two models by British sportscar manufacturer TVR. The bore was 94.0 mm (3.70 in) and the stroke was 90.0 mm (3.54 in). These models, the Griffith and Chimaera used the 5 litre unit in their top-end specifications. The factory quotes up to 340 bhp (254 kW) and 350 lb·ft (475 N·m) of torque.
Moreover, in the mid-1980s, hot rodders discovered the 215 could be stretched to as much as 305 cu in (5 l), using the Buick 300 crankshaft, new cylinder sleeves, and an assortment of non-Buick parts.It could also be fitted with high-compression cylinder heads from the Morgan +8. Using the 5 liter Rover block and crankshaft, a maximum displacement of 317.8 cu in (5,208 cc) is theoretically possible.