This might help you, but you need to confirm the sizes listed by actual measurements of your parts (is your swing arm shaft 20mm?).
Joe
http://www.ktmworld.com/ktm_oem_parts_schematic.asp
select 1998 400 RXC-E(USA)
select Swing Arm 400-620LC '97
MICROFICHE - OEM PARTS
Year: 1998
Model: 400 RXC-E USA (087166)
Parts: SWINGARM - SWING ARM 400-620 LC4 `97
If a part is not listed below or not priced then please call us.
# KTM Part Description Price Qty
12 54603014100 SWINGARM BOLT KPL. L=253 $32.97
14 50230211000 BRAKE HOSE GUIDE 89 $5.06
15 54603015000 SELF LOCKING NUT M14X1,5 WS=19 $5.16
16 54403135000 PLASTIC CAP SFL10 $1.93
30 58404030344 SWINGARM CPL. LC4 03 $565.22
38 54611076100 RETAIN.CLAMP FOR BRAKE HOSE96 $1.15
39 0010050103 SPECIAL SCREW M 5,0X10 $0.92
40 50203081700 BUSHING SLEEVE 15X20X38,75 $18.43
41 59004031000 NEEDLE BUSH HK2012V $7.08
42 54603036000 STOP DISK 22,2X31,7X1 $1.63
43 0760253270 SHAFT SEAL RING 25X32X7 $5.63
44 54603090000 BUCKET F.SHAFTSEALRING 15X25X9 $12.38
60 58307060000 CHAINGUARD SMALL 96 $24.43
62 58307060250 CHAINGUARD LARGE 03 $7.11
64 0125050003 WASHER DIN0125-A 5,3 $0.31
65 20012062055 HOLLOW RIVET TWO PARTS $1.03
67 0125060003 WASHER DIN0125-A 6,4 $0.27
68 0985060003 SELF LOCK. NUT DIN0985-M 6 $0.27
71 72210079000 BUCKET $2.24
72 0015060103 HH COLLAR SCREW M 6X10 WS=8 $1.25
73 58307073000 CHAIN SLIDING GUARD DUKE94 $27.14
85 54607066100 CHAIN GUIDE REAR 94 $28.15
86 50207070044 RETAINING PLATE CHAIN GUIDE94 $21.06
89 0015060553 HH COLLAR SCREW M 6X55 WS=8 $1.31
90 0015060503 HH COLLAR SCREW M 6X50 WS=8 $1.31
91 0015060163 HH COLLAR SCREW M 6X16 WS=8 $0.46