Honestly? I'll prolly get flamed for this but oh well...

If ur car won't see 1000 miles a year, and an automatic tranny is going behind it, a tach isn't really one of your high priorities right now...

My advise:

Sound: Get a pair of headers, then weld some pipes to those, then put a good muffler like a 40 Series Flowmaster, if u want it to be a little quieter get 50 Series...

Performance...

There's always obvious ways to up that power...

Heads (new or u can get yours machined for flow), intake, cam (a hot cam can really wake up a motor, be careful. There is such thing as TOO MUCH cam), If u want to pull the motor a part, u can put a flat top piston in there if there isnt already...That will up the compression thus making more power.
Carb: i think the formula is
rpm x displacement
-------------------------
3456

For example... if u were running a 350 up to 5,000 rmp maximum it would be:

5,000 x 350 / 3456 = 506 CFM

Of course, if u go with more radical parts u want more radical carburetor but Ill let someone who knows a little more about CFM explain how to compensate accordingly. Good luck! I hope my advice is as on target as anyone else's.