i take it you're replacing 'turbo' power with displacement torque yeah?
what about these engines? all are a proven engineered combo into a 1200.

12A turbo
CA18DET
grumpy SR20DE/T
VG20DET
VG30DE

or if you're a bit of a frankenstein builder, what about the 7AF toyota bottom end (1.8L) with a 20V 4AG head. they are the same engine but one is 1.6 and one is 1.8 (like the L16 and L18). the only mod needed is to machine the tensioner pulley 2.0mm in diameter to make the timing belt fit. then you'd have a rev-happy 1.8L with 5 valves per cylinder and quad throttles. mmmm...twin cam bark.....

if you want to get something big cube though, none of this will help.

why not look at the toyota century 3.4L 'mini-hemi' all alloy pushrod V8? they're lighter than an SR20DET....and take a supra 5spd with a dellow bellhousing.

the VG30DE would be a good conversion too.

what about the 1MZFE? no, not the 1UZFE, the 1MZFE. the 3.0L V6 out of the 97-98 camry's...basically a 1UZFE with 2 cylinders cut off. HSV killers. with a sump mod (or not...?) to convert from east west to north south and another dellow bellhousing for the supra 5spd, it would be economical, light and VERY powerful for a 1200.