Depemding on year a 318 can be mechanical or hydro clutch. Bells should be same engine bolt patterns, except for 1 bolt on some applications. Most bells are drilled for a couple of trans bolt patterns. The input shaft bearing retainer hole can be a problem, some bells have a smaller hole. I think the most common sizes were 4.354", 4.807", 4.85" & 5.125", a considerable difference.

Input shaft on my 318 Poly/NP435 4 speed was 1" x 10 spline, can't remember the other common fine spline size, but thinking it's 23 spline?

Slant six flywheel bolt spacing [6 bolt] is different from 318 V8 [6 bolt] spacing. You also have to match flywheel to cranshaft flange. 318-340-383-440 use a common flywheel bolt pattern. RB engines [440-6 pack] use a different flywheel.

'74-'80 slant six 9-1/4" clutch and '74-'78 slant six 10" clutch have a 10-5/8" mounting bolt circle, '74-'78 318 10-1/2" clutch & 74 360 11" clutch are 11-5/8" mounting bolt circle.

All '70-'74 w/ 10-1/2" , all '70-'78 w/ 11" clutch clutch use a 10 tooth starter, 130 tooth ring gear. All '69 w/ 11" clutch [except Hemi] use 10 tooth starter, 143 tooth ring gear.

'74-'78 318 & '74 400 use the same flywheel.