The engine/wheels/suspension would be Street Modified legal, but the stripped interior is going to bump you out of that. Which leaves a Prepared or Modified class.
Most of Prepared is for vehicles running the engine it came with. There is one class, XP (see page 195 of rulebook) that is pretty much wide open and would allow the 1.8 swap. It still follows the rules of Prepared (section 17), but anything noted in the appendix supercedes the rules in section 17. Section 7 on page 196 covers the permitted engines in XP. The only real requirement is min weight:
Quote:
9. Minimum Weights
a. Engine Classifications
1. 4-stroke cycle and 2-stroke cycle, naturally aspirated, internal combustion
engines will be classified on the basis of actual piston displacement.
2. Turbocharged or supercharged versions of all engines will be classified
on a basis of 1.4 times the actual displacement.
3. Rotary Engines (Wankel): These units will be classified on the basis
of a piston displacement equivalent to twice the volume determined
by the difference between the maximum and minimum capacity of
the working chamber, times the number of rotors.
b. Minimum Weight Calculations
All listed weights are without driver. All weights are calculated based
on displacement as listed above. Example: Weight for a RWD car w/
1796 cc Turbo engine behind the driver is 1200 + [(1.796 x 1.4) x (200
+ 20)] = 1753 lbs.
Engine displacement less than 4.0L
FWD.................................................................. 1200 lbs. + 150 lbs. per liter
RWD................................................................. 1200 lbs. + 200 lbs. per liter
AWD.................................................................. 1200 lbs. + 250 lbs. per liter
Engine displacement of 4.0L or greater
FWD.................................................................. 1200 lbs. + 130 lbs. per liter
RWD................................................................. 1200 lbs. + 180 lbs. per liter
AWD.................................................................. 1200 lbs. + 250 lbs. per liter
Since it's a 2.0, you required weight is 1200lbs + (2L * 1.4 correction)*150lbs/L = 1620lbs. All Prep classes allow a stripped interior.
If it doesn't fit into prepared, the other option would likely be E Modified which covers unrestricted turbo stuff. But chances are if it's derived from a street car you can run it in XP.