I need to know what size v8 gm motor is - 1981 Chevrolet Corvette

This 4.3 V6 is just a 350 V8 with 2 cylinders missing and even a V8 trans will fit/interchange physically being the same bolt pattern and size. If it's the same shift pattern and both transmissions are overdrive transmissions, yes, it will interchange. If it's GM, it'll swap. From 1988 the automatic transmissions have a multi bolt pattern and Pontiac, Caddy, Olds and Chevy, all will bolt up.

You can copy down the entire vin on your car and call Chevrolet. They will know as long as it still has the original engine.

I guess my first question would be - what are your plans for the car ?
Totally stock, modified, or race ?
Totally stock would be the most valuable in terms of resale. Modified or race would limit the number and type of possible buyers.
It had a straight 6 cyl 250 - a 350 V8 - or 400 V8 when new. The VIN would tell you want the original engine was. And this was before GM swapped engines between brands. So the V8 engines were Pontiac built. The Pontiac 6 cyl was overhead cam.

FIRING ORDERS NOTE: To avoid confusion, remove and tag the spark plug wires one at a time, for replacement. If a distributor is not keyed for installation with only one orientation, it could have been removed previously and rewired. The resultant wiring would hold the correct firing order, but could change the relative placement of the plug towers in relation to the engine. For this reason it is imperative that you label all wires before disconnecting any of them. Also, before removal, compare the current wiring with the accompanying illustrations. If the current wiring does not match, make notes in your book to reflect how your engine is wired. Fig. 1: GM (Cadillac) 250 (4.1L) V8 GM (Cadillac) 273 (4.5L) V8 Engine firing order: 1-8-4-3-6-5-7-2 Distributor rotation: counterclockwise Fig. 2: GM (Oldsmobile) 307 (5.0L) V8 GM (Oldsmobile) 350 (5.7L) V8 w/EFI Engine firing order: 1-8-4-3-6-5-7-2 Distributor rotation: counterclockwise Fig. 3: GM (Buick) 252 (4.1L) V6 Engine firing order: 1-6-5-4-3-2 Distributor rotation: clockwise Fig. 4: GM (Cadillac) 368, 425, 472, 500 V8 Engine firing order: 1-5-6-3-4-2-7-8 Distributor rotation: clockwise Fig. 5: GM (Cadillac) 429 V8 Engine firing order: 1-8-7-2-6-5-4-3 Distributor rotation: clockwise

All the starters are the same for the V8's in that year on GM motors, They gave you the wrong starter

What are you doing? GM, DODGE, FORD? This is good for GMs. From the 60's up to 99. As long as there is a round distrubitor on a GM V8, this diagram should be all you need.

F350 V8-351 5.8L (gasoline) V8-460 7.5L(gasoline)

You didn't post your engine size so please use the appropriate diagram:




GM (Cadillac) 250 (4.1L) V8 .GM (Cadillac) 273 (4.5L) V8 .GM (Oldsmobile) 307 (5.0L) V8 .GM (Oldsmobile) 350 (5.7L) V8 w/EFI.Engine firing order: 1-8-4-3-6-5-7-2 .Distributor rotation: counterclockwise





GM (Buick) 252 (4.1L) V6 .Engine firing order: 1-6-5-4-3-2.Distributor rotation: clockwise





GM (Cadillac) 368, 425, 472, 500 V8.Engine firing order: 1-5-6-3-4-2-7-8.Distributor rotation: clockwise





GM (Cadillac) 429 V8.Engine firing order: 1-8-7-2-6-5-4-3.Distributor rotation: clockwise

Need to know the engine size. You have these choices:
4.2 L Essex V6
4.9 L inline-6
302 CID Windsor V8
351 CID Windsor V8
4.6 L Triton V8
5.4 L Triton V8
6.8 L Triton V10
7.3 L Power Stroke V8
6.0 L Power stroke V8
TD

Not sure what you mean by 8-6-4 but this will help you. Pick the correct one for your application:



GM (Cadillac) 250 (4.1L) V8 .GM (Cadillac) 273 (4.5L) V8 .GM (Oldsmobile) 307 (5.0L) V8 .GM (Oldsmobile) 350 (5.7L) V8 w/EFI.Engine firing order: 1-8-4-3-6-5-7-2 .Distributor rotation: counterclockwise



GM (Cadillac) 368, 425, 472, 500 V8.Engine firing order: 1-5-6-3-4-2-7-8.Distributor rotation: clockwise




GM (Cadillac) 429 V8.Engine firing order: 1-8-7-2-6-5-4-3.Distributor rotation: clockwise