NV-4500 should give OD. Be careful, normal 5 speed trans' that have OD added where 4th gear was located, NP-540, Clark, IHC, etc., do so by removing that gear, thus leaving a large gap in ratios just under direct. A two speed rear helps sometimes.

Eaton makes several OD trans, however many use SAE mounting systems. There are, however, bellhousing adapters that go from SAE engines to conventional flat trans' mounting systems. I have several if you would like a px.

Ed

'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.